Monday, June 3, 2019

Genetics of Skin Cancer (PDQ®) 2/4 —Health Professional Version - National Cancer Institute

Genetics of Skin Cancer (PDQ®)—Health Professional Version - National Cancer Institute

National Cancer Institute

Genetics of Skin Cancer (PDQ®)–Health Professional Version

Squamous Cell Carcinoma

Introduction

Squamous cell carcinoma (SCC) is the second most common type of skin cancer and accounts for approximately 20% of cutaneous malignancies. Although most cancer registries do not include information on the incidence of nonmelanoma skin cancer (NMSC), annual incidence estimates range from 1 million to 5.4 million cases in the United States.[1-3] Multiple studies indicate an increased risk of SCC after a first NMSC; a meta-analysis and review of 45 studies estimated that after a primary SCC diagnosis, 13.3% of individuals would develop a second SCC (95% confidence interval [CI], 7.4%–22.8%).[4]
Mortality is rare from this cancer; however, the morbidity and costs associated with its treatment are considerable.

Risk Factors for Squamous Cell Carcinoma

Sun exposure and other risk factors

Sun exposure is the major known environmental factor associated with the development of skin cancer of all types; however, different patterns of sun exposure are associated with each major type of skin cancer.[5-7] Unlike basal cell carcinoma (BCC), SCC is associated with chronic exposure, rather than intermittent intense exposure to ultraviolet (UV) radiation. Occupational exposure is the characteristic pattern of sun exposure linked with SCC.[5] (Refer to the PDQ summary on Skin Cancer Prevention for more information about sun and other environmental and therapeutic exposures as risk factors for skin cancer in the general population.) Other environmental agents associated with SCC risk include tanning beds, arsenic, therapeutic radiation (such as psoralen and ultraviolet A therapy for psoriasis), and immunosuppression.[8-14]

Characteristics of the skin

Like melanoma and BCC, SCC occurs more frequently in individuals with lighter skin than in those with darker skin.[5,15] A case-control study of 415 cases and 415 controls showed similar findings; relative to Fitzpatrick type I skin, individuals with increasingly darker skin had decreased risks of skin cancer (odds ratios [ORs], 0.6, 0.3, and 0.1, for Fitzpatrick types II, III, and IV, respectively).[16] (Refer to the Pigmentary characteristics section in the Melanoma section of this summary for a more detailed discussion of skin phenotypesbased upon pigmentation.) The same study found that blue eyes and blond/red hair were also associated with increased risks of SCC, with crude ORs of 1.7 (95% CI, 1.2–2.3) for blue eyes, 1.5 (95% CI, 1.1–2.1) for blond hair, and 2.2 (95% CI, 1.5–3.3) for red hair.
However, SCC can also occur in individuals with darker skin. An Asian registry based in Singapore reported an increase in skin cancer in that geographic area, with an incidence rate of 8.9 per 100,000 person-years. Incidence of SCC, however, was shown to be on the decline.[15] SCC is the most common form of skin cancer in black individuals in the United States and in certain parts of Africa; the mortality rate for this disease is relatively high in these populations.[17,18] Epidemiologic characteristics of, and prevention strategies for, SCC in those individuals with darker skin remain areas of investigation.
Freckling of the skin and reaction of the skin to sun exposure have been identified as other risk factors for SCC.[19] Individuals with heavy freckling on the forearm were found to have a 14-fold increase in SCC risk if freckling was present in adulthood, and an almost threefold risk if freckling was present in childhood.[19,20] The degree of SCC risk corresponded to the amount of freckling. In this study, the inability of the skin to tan and its propensity to burn were also significantly associated with risk of SCC (OR of 2.9 for severe burn and 3.5 for no tan).
The presence of scars on the skin can also increase the risk of SCC, although the process of carcinogenesis in this setting may take years or even decades. SCCs arising in chronic wounds are referred to as Marjolin’s ulcers. The mean time for development of carcinoma in these wounds is estimated at 26 years.[21] One case report documents the occurrence of cancer in a wound that was incurred 59 years earlier.[22]

Immunosuppression

Immunosuppression also contributes to the formation of NMSCs. Among solid-organ transplant recipients, the risk of SCC is 65 to 250 times higher, and the risk of BCC is 10 times higher than that observed in the general population, although the risks vary with transplant type and with the immunosuppressive agent used.[23-26] NMSCs in high-risk patients (solid-organ transplant recipients and chronic lymphocytic leukemia patients) occur at a younger age, are more common and more aggressive, and have a higher risk of recurrence and metastatic spread than these cancers do in the general population.[27,28] Additionally, there is a high risk of second SCCs.[29,30] In one study, more than 65% of kidney transplant recipients developed subsequent SCCs after their first diagnosis.[29] Among Medicare patients with an intact immune system, BCCs occur as frequently as SCCs;[3] in transplant patients, SCCs outnumber BCCs by a 2:1 ratio.

Personal history of nonmelanoma and melanoma skin cancer

A personal history of BCC or SCC is strongly associated with subsequent SCC. A study from Ireland showed that individuals with a history of BCC had a 14% higher incidence of subsequent SCC; for men with a history of BCC, the subsequent SCC risk was 27% higher.[31] In the same report, individuals with melanoma were also 2.5 times more likely to report a subsequent SCC. There is an approximate 20% increased risk of a subsequent lesion within the first year after a skin cancer has been diagnosed. The mean age of occurrence for these NMSCs is the middle of the sixth decade of life.[32-37]
A Swedish study of 224 melanoma index cases and 944 of their first-degree relatives (FDRs) from 154 CDKN2A wild-type families and 11,680 matched controls showed that personal and family histories of melanoma increased the risk of SCC, with relative risks (RRs) of 9.1 (95% CI, 6.0–13.7) for personal history and 3.4 (95% CI, 2.2–5.2) for family history.[38]

Family history of squamous cell carcinoma or associated premalignant lesions

Although the literature is scant on this subject, a family history of SCC may increase the risk of SCC in FDRs. In an independent survey-based study of 415 SCC cases and 415 controls, SCC risk was increased in individuals with a family history of SCC (adjusted OR, 3.4; 95% CI, 1.0–11.6), even after adjustment for skin type, hair color, and eye color.[16] This risk was elevated to an OR of 5.6 in those with a family history of melanoma (95% CI, 1.6–19.7), 9.8 in those with a family history of BCC (95% CI, 2.6–36.8), and 10.5 in those with a family history of multiple types of skin cancer (95% CI, 2.7–29.6). Review of the Swedish Family Center Database showed that individuals with at least one sibling or parent affected with SCC, in situ SCC (Bowen disease), or actinic keratosis had a twofold to threefold increased risk of invasive and in situ SCC relative to the general population.[39,40] Increased number of tumors in parents was associated with increased risk to the offspring. Of note, diagnosis of the proband at an earlier age was not consistently associated with a trend of increased incidence of SCC in the FDR, as would be expected in most hereditary syndromes because of germline pathogenic variants. Further analysis of the Swedish population-based data estimates genetic risk effects of 8% and familial shared-environmental effects of 18%.[41] Thus, shared environmental and behavioral factors likely account for some of the observed familial clustering of SCC.
A study on the heritability of cancer among 80,309 monozygotic and 123,382 dizygotic twins showed that NMSCs have a heritability of 43% (95% CI, 26%–59%), suggesting that almost half of the risk of NMSC is caused by inherited factors.[42] Additionally, the cumulative risk of NMSC was 1.9-fold higher for monozygotic than for dizygotic twins (95% CI, 1.8–2.0).[42]

Syndromes and Genes Associated With a Predisposition for Squamous Cell Carcinoma

Major genes have been defined elsewhere in this summary as genes that are necessary and sufficient for disease, with important pathogenic variants of the gene as causal. The disorders resulting from single-gene pathogenic variants within families lead to a very high risk of disease and are relatively rare. The influence of the environment on the development of disease in individuals with these single-gene disorders is often very difficult to determine because of the rarity of the genetic variant.
Identification of a strong environmental risk factor—chronic exposure to UV radiation—makes it difficult to apply genetic causation for SCC of the skin. Although the risk of UV exposure is well known, quantifying its attributable risk to cancer development has proven challenging. In addition, ascertainment of cases of SCC of the skin is not always straightforward. Many registries and other epidemiologic studies do not fully assess the incidence of SCC of the skin owing to: (1) the common practice of treating lesions suspicious for SCC without a diagnostic biopsy, and (2) the relatively low potential for metastasis. Moreover, NMSC is routinely excluded from the major cancer registries such as the Surveillance, Epidemiology, and End Results registry.
With these considerations in mind, the discussion below will address genes associated with disorders that have an increased incidence of skin cancer.
Characteristics of the major hereditary syndromes associated with a predisposition to SCC are described in Table 5 below.
Table 5. Hereditary Syndromes Associated with Squamous Cell Carcinoma of the Skin
ConditionGene(s)Clinical Testing AvailabilityaPathway
aFor more information on genetic testing laboratories, refer to the NIH Genetic Testing Registry.
Bloom syndromeBLM/RECQL3Sister chromatid exchangeBLMChromosomal stability
Chediak-Higashi syndromeLYSTLYSTLysosomal transport regulation
Dyskeratosis congenitaDKC1TERCTINF2NHP2/NOLA2NOP10/NOLA3TERTWRAP53C16orf57RTEL1DKC1, TERC, TINF2, NHP2, NOP10, TERTTelomeremaintenance and trafficking
Dystrophic epidermolysis bullosa(autosomal dominant and autosomal recessivesubtypes)COL7A1COL7A1Collagen anchor of basement membrane to dermis
Elejalde diseaseMYO5ANoPigment granule transport
Epidermodysplasia verruciformisEVER1/TMC6EVER2/TMC8NoSignal transduction in endoplasmic reticulum
Fanconi anemiaFANCAFANCBFANCC,FANCD1/BRCA2FANCD2FANCE,FANCFFANCG/XRCC9FANCI,FANCJ/BRIP1/BACH1FANCL,FANCMFANCN/PALB2FANCO/RAD51CFANCP/SLX4/BTBD12FANCQ/ERCC4/XPFFANCS/BRCA1Chromosomal breakage testing; BRIP1, FANCA, FANCC, FANCE, FANCF, FANCG, PALB2, BRCA1, BRCA2, ERCC4, RAD51C, SLX4DNA repair
Griscelli syndrome(type 1, type 2, and type 3)MYO5ARAB27AMLPHRAB27APigment granule transport
Hermansky-Pudlak syndromeHPS1HPS3HPS4HPS5HPS6,HPS7/DTNBP1HPS8/BLOC1S3HPS1, HPS3, HPS4, HPS7Melanosomal and lysosomal storage
Hermansky-Pudlak syndrome, type 2AP3B1NoMelanosomal and lysosomal storage
Huriez syndromeUnknown; Locus 4q23NoUnknown
Junctional epidermolysis bullosaLAMA3LAMB3LAMC2COL17A1LAMA3, LAMB3, LAMC2, COL17A1Connective tissue
Multiple self-healing squamous epithelioma (Ferguson-Smith syndrome)TGFBR1NoGrowth factor signaling
Oculocutaneous albinism (type IA, type IB, type II, type III, type IV, type V, type VI, and type VII)TYROCA2TYRP1SLC45A2/MATP/OCA4, Locus 4q24, SLC24A5C10Orf11TYR, OCA2, TYRP1Melanin synthesis
Rothmund-Thomson syndromeRECQL4C16orf57RECQL4Chromosomal stability
Werner syndromeWRN/RECQL2NoChromosomal stability
Xeroderma pigmentosum(complementation group A, group B, group C, group D, group E, group F, and group G)XPAXPB/ERCC3XPCXPD/ERCC2,XPE/DDB2XPF/ERCC4,XPG/ERCC5XPA, XPCNucleotide excision repair
Xeroderma pigmentosum variantPOLH/XPVNoError-prone polymerase

Xeroderma pigmentosum

Xeroderma pigmentosum (XP) is a hereditary disorder of nucleotide excision repair that results in cutaneous malignancies in the first decade of life.[43Affected individuals have an increased sensitivity to sunlight, resulting in a markedly increased risk of SCCs, BCCs, and melanomas. One report found that NMSC was increased 150-fold in individuals with XP; for those younger than 20 years, the prevalence has been estimated to be 5,000 to 10,000 times what would be expected in the general population.[44,45]
The natural history of this disease begins in the first year of life, when sun sensitivity becomes apparent, and xerosis (dry skin) and pigmentary changes may occur in the sun-exposed skin. About one-half of XP patients have a history of severe burning on minimal sun exposure. Other XP patients do not have this reaction but develop freckle-like pigmentation before age 2 years on sun-exposed sites. These manifestations progress to skin atrophy and formation of telangiectasias. Approximately one-half of people with this disorder will develop NMSCs, and approximately one-quarter of these individuals will develop melanoma.[44] In the absence of sun avoidance, the median age of diagnosis for any skin cancer is 8 to 9 years.[44-46] On average, NMSC occurs at a younger age than melanoma in the XP population.[45]
Noncutaneous manifestations of XP include ophthalmologic and neurologic abnormalities. Disorders of the cornea and eyelids associated with this disorder are also linked to exposure to UV radiation and include keratitis, corneal opacification, ectropion or entropion, hyperpigmentation of the eyelids, loss of eyelashes, and cancer, including conjunctival and corneal cancers.[47] About 25% of the XP patients examined at the National Institutes of Health (NIH) between 1971 and 2009 had progressive neurological degeneration.[45] Features included microcephaly, progressive sensorineural hearing loss, diminished deep tendon reflexes, seizures, and cognitive impairment. Neurological degeneration, which is most commonly observed in individuals with complementation groups XPA and XPD, was associated with a shorter lifespan (median age of death was 29 years in individuals with neurological degeneration and 37 years in individuals without neurological degeneration).[45] De Sanctis-Cacchione syndrome is found in a subgroup of XP patients, who exhibit severe neurologic manifestations, dwarfism, and delayed sexual development. A variety of noncutaneous neoplasms, most notably SCC of the tip of the tongue, central nervous system cancers, and lung cancer in smokers, have been reported in people who have XP.[44,48] The RR for these cancers is estimated to be about 50-fold higher than in the general population.[44]
The inheritance for XP is autosomal recessive. Seven complementation groups have been associated with this disorder. About 40% of the XP cases seen at the NIH were XPC. ERCC2(XPD) pathogenic variants were present in about 20%. Complementation group A, due to a pathogenic variant in XPA, accounts for approximately 10% of cases.[45] Other variant genes in this disorder include ERCC3 (XPB), DDB2 (XPE), ERCC4 (XPF), and ERCC5 (XPG). An XPH group had been described but is now considered to be a subgroup of the XPD group.[49Heterozygotes for pathogenic variants in XP genes are generally asymptomatic.[50Founder pathogenic variants in XPA (R228A) and XPC (V548A fs X572) have been identified in North African populations, and a founder pathogenic variant in XPC resulting in a splice alteration (IVS 12-1G>C) has been found in an East African (Mahori) population. It has been proposed that direct screening for these pathogenic variants would be appropriate in these populations.[51-54] A founder pathogenic variant at the 3’ splice acceptor site of intron 3 in the XPA gene is present in approximately 1% of the population in Japan representing nearly 1 million people.[55]
The function of the XP genes is to recognize and repair photoproducts from UV radiation. The main photoproducts are formed at adjacent pyrimidines and consist of cyclobutane dimers and pyrimidine-pyrimidone (6-4) photoproducts. The product of XPC is involved in the initial identification of DNA damage; it binds to the lesion to act as a marker for further repair. The DDB2 (XPE) protein is also part of this process and works with XPC. The XPAgene product maintains single-strand regions during repair and works with the TFIIH transcription factor complex. The TFIIH complex includes the gene products of both ERCC3(XPB) and ERCC2 (XPD), which function as DNA helicases in the unwinding of the DNA. The ERCC4 (XPF) and ERCC5 (XPG) proteins act as DNA endonucleases to create single-strand nicks in the 5’ and 3’ sides of the damaged DNA with resulting excision of about 28 to 30 nucleotides, including the photoproduct. DNA polymerases replace the lesion with the correct sequence, and a DNA ligase completes the repair.[43,56]
An XP variant that is associated with pathogenic variants in POLH (XPV) is responsible for approximately 10% of reported cases.[57] This gene encodes for the error-prone bypass polymerase (polymerase eta) which, unlike other genes associated with XP, is not involved in nucleotide excision repair. People with polymerase eta pathogenic variants have the same cutaneous and ocular findings as other XP patients but do not have progressive neurologic degeneration.[58] A founder pathogenic variant resulting in a deletion of exon10 was seen in 16 of 16 individuals from ten Tunisian consanguineous families.[59]
Work on genotype -phenotype correlations among the XP complementation groups continues; however, evidence suggests that the specific pathogenic variant may have more influence on the phenotype than the complementation group.[43,60] The main distinguishing features appear to be the presence or absence of burning on minimal sun exposure, skin cancer, and progressive neurologic abnormalities. All complementation groups are characterized by the presence of cutaneous neoplasias, but skin cancers may be more common in XPC, XPE, and XPV groups.[60]. There is additional clinical variation within each complementation group. Mild to severe neurologic impairment has been described in individuals with XPA pathogenic variants. Individuals with XPA pathogenic variants in the DNA binding region (amino acids 98–219) may have a more severe presentation that includes neurological findings.[61] Individuals within the XPC complementation group have higher incidences of ocular damage.[60] A very small number of people in the XPB, XPD, and XPG complementation groups have been identified as having xeroderma pigmentosum-Cockayne syndrome (XP-CS) complex. These individuals have characteristics of both disorders, including an increased predisposition to cutaneous neoplasms and developmental delay, visual and hearing impairment, and central and peripheral nervous system dysfunction. It should be noted that people with Cockayne syndrome without XP do not appear to have an increased cancer risk.[62] Similarly, trichothiodystrophy (TTD) is another genetic disorder that can occur in combination with XP. Individuals affected solely with TTD do not appear to have an increased cancer incidence, but some affected with XP/TTD have an increased risk of cutaneous neoplasia. The complementation groups connected with XP/TTD (XPD and XPB) and XP-CS (XPB, XPD, and XPG) are associated with defects in both transcription-coupled nucleotide excision repair and global genomic nucleotide excision repair. In contrast, XP complementation groups C and E have defects only in global genomic nucleotide excision repair.[43,63] In addition, individuals in the XPA, XPD and XPG groups may exhibit severe neurologic abnormalities without symptoms of Cockayne syndrome or TTD. Cerebro-oculo-facio-skeletal syndrome, which has been described with some ERCC2 (XPD) or XP-CS pathogenic variants, does not appear to confer an increased risk of skin cancer.[64-67]
The diagnosis of XP is made on the basis of clinical findings and family history. Functional assays to assess DNA repair capabilities after exposure to radiation have been developed, but these tests are currently not clinically available in the United States. Clinical genetic testing using sequence analysis to identify pathogenic variants is available for multiple XP-associated genes; the list can be found at the NIH Genetic Testing Registry.

Multiple self-healing squamous epitheliomata (Ferguson-Smith syndrome)

Multiple self-healing squamous epitheliomata (MSSE), or Ferguson-Smith syndrome, first described in 1934, is characterized by invasive skin tumors that are histologically identical to sporadic cutaneous SCC, but they resolve spontaneously without intervention. Linkage analysis of affected families showed association with the long arm of chromosome 9, and haplotype analysis localized the gene to 9q22.3 between D9S197 and D9S1809.[68] Transforming growth factor beta-receptor 1 (TGFBR1) was identified through next-generation sequencing as the gene responsible for MSSE. Loss-of-function pathogenic variants in TGFBR1 have been identified in 18 of 22 affected families.[69] Gain-of-function variants in TGFBR1 are associated with unrelated Marfan-like syndromes, such as Loeys-Dietz syndrome, which have no described increase in skin cancer risk.
Somatic loss of heterozygosity in Ferguson-Smith–related SCC has been demonstrated at this genomic location, suggesting that TGFBR1 can act as a tumor suppressor gene.[70] The long arm of chromosome 9 has also been a site of interest in sporadic SCC. Up to 65% of sporadic SCCs have been found to have loss of heterozygosity at 9q22.3 between D9S162 and D9S165.[70]

Oculocutaneous albinism

Albinism is a major risk factor for skin cancer in individuals of African ancestry.[18,71] One report describing a cohort of 350 albinos in Tanzania found 104 cutaneous cancers; of these, 100 were SCCs, three were BCCs, and one was melanoma.[72] The median age for this population was 10 years. Similar proportions of skin cancer diagnoses were observed in a Nigerian population, with 62% of dermatological malignancies diagnosed as SCC, 16% as melanoma, and 8% as BCC.[18] Of note, some melanomas found in individuals with albinism do contain melanin.[73]
SCC occurring at extremely early ages is a hallmark of oculocutaneous albinism. In a cohort of nearly 1,000 Nigerian patients with albinism, all had malignant or premalignant cutaneous lesions by age 20 years.[74]
Two types of oculocutaneous albinism are known to be associated with increased risk of SCC of the skin. Oculocutaneous albinism type 1, or tyrosinase-related albinism, is caused by pathogenic variants in the tyrosinase gene, TYR, located on the long arm of chromosome 11. This type of albinism accounts for about one-half of cases in individuals of Caucasian ancestry.[75] The OCA2 gene, also known as the P gene, is altered in oculocutaneous albinism type 2, or tyrosinase-positive albinism. Both disorders are autosomal recessive, with frequent compound heterozygosity.
Tyrosinase acts as the critical enzyme in the synthesis of melanin in melanocytes. A variant in this gene in oculocutaneous albinism type 1 produces proteins with minimal to no activity, corresponding to the OCA1B and OCA1A phenotypes, respectively. Individuals with OCA1B have light skin, hair, and eye coloring at birth but develop some pigment during their lifetimes, while the coloring of those with OCA1A does not darken with age.
The gene product of OCA2 is a protein found in the membrane of melanosomes. Its function is unknown, but it may play a role in maintaining the structure or pH of this environment.[76] Murine models with variants in this gene had significantly decreased melanin production compared with normal controls.[77] In one international study of individuals with albinism, biallelic variants in OCA2 were found in 17% of participants.[78]
Genetic variants in SLC45A2 (MATP associated with OCA4), SLC24A5 (associated with OCA6), and TYRP1 (tyrosinase-related protein 1 associated with OCA3) are associated with less common types of oculocutaneous albinism. Reported incidences for these genes in an international population of patients with albinism are 7% for SLC45A2, 1% for TYRP1, and less than 0.5% for SLC24A5.[78SLC45A2 is found in 24% of oculocutaneous albinism cases in Japan, making it the most common type of albinism among Japanese individuals with identifiable variants.[79] A study of 22 individuals of Italian ancestry without pathogenic variants in TYROCA2, or TYRP1 found 5 individuals with biallelic variants in SLC45A2, 4 of whom met clinical criteria for a diagnosis of oculocutaneous albinism.[80] Collectively, more than 600 unique ocular albinism–related genetic variants have been identified.[81] The increased risk of SCC of the skin in people with these variants has not been quantified. It is generally assumed to be similar to other types of albinism. Of note, a meta-analysis demonstrated that the SLC45A2 p.Phe374Leu variant was protective for melanoma, with an OR of 0.41 (95% CI, 0.33–0.50; P = 3.50 x 10-17).[82] However, at this time, it should be noted that clinical testing is not routinely performed for protective variants.
Additional genes associated with oculocutaneous albinism have been found in small numbers of patients. OCA5, located on chromosome 4q24, has been identified in a Pakistani family, whereas OCA6 appears to be caused by pathogenic variants in SLC24A5 on chromosome 15q21.[83-85] Pathogenic variants in C10orf11 (LRMDA) cause OCA7, which has been found in patients from the Faroe Islands and Denmark.[86] Small numbers of pathogenic variant carriers have been reported to date. One woman with OCA6 had actinic keratosis, but the incidence of skin cancers in these populations is unknown.
Table 6. Types of Oculocutaneous Albinism (OCA)
TypeSubtypeGeneReporting PopulationAvailability of Clinical Test
OCA Type 11ATYRJapanese,[87] Chinese,[88] White [89-93]Yes
1BTYR
OCA Type 2 OCA2 (P gene)African,[94,95] African American,[96] Native American [97]Yes
OCA Type 3 TYRP1African [98]Yes
OCA Type 4 SLC45A2 (MATP)Japanese,[79] Italian,[80] German [99]Yes
OCA Type 5 OCA5Pakistani [83]Not in the United States
OCA Type 6 SLC24A5Chinese,[84] African,[100] European,[85] Indian [101]Yes
OCA Type 7 C10orf11(LRMDA)Faroe Islands,[86] Denmark [86]Yes

Other albinism syndromes

A subgroup of albinism includes people who exhibit a triad of albinism, prolonged bleeding time, and deposition of a ceroid substance in organs such as the lungs and gastrointestinal tract. This syndrome, known as Hermansky-Pudlak syndrome, is inherited in an autosomal recessive manner but may have a pseudodominant inheritance in Puerto Rican families, owing to the high prevalence in this population.[102] The underlying cause is believed to be a defect in melanosome and lysosome transport. A number of pathogenic variants at disparate loci have been associated with this syndrome, including HPS1HPS3HPS4HPS5HPS6HPS7 (DTNBP1), HPS8 (BLOC1S3), and HPS9 (PLDN).[103-110] Pigmentation characteristics can vary significantly in this disorder, particularly among those with HPS1pathogenic variants, and patients report darkening of the skin and hair as they age. In a small cohort of individuals with HPS1 variants, 3 out of 40 developed cutaneous SCCs, and an additional 3 had BCCs.[111] Hermansky-Pudlak syndrome type 2, which includes increased susceptibility to infection resulting from congenital neutropenia, has been attributed to defects in AP3B1.[112]
Two additional syndromes are associated with decreased pigmentation of the skin and eyes. The autosomal recessive Chediak-Higashi syndrome is characterized by eosinophilic, peroxidase-positive inclusion bodies in early leukocyte precursors, hemophagocytosis, increased susceptibility to infection, and increased incidence of an accelerated phase lymphohistiocytosis. Pathogenic variants in the LYST gene underlie this syndrome, which is often fatal in the first decade of life.[113-115]
Griscelli syndrome, also inherited in an autosomal recessive manner, was originally described as decreased cutaneous pigmentation with hypomelanosis and neurologic deficits, but its clinical presentation is quite variable. This combination of symptoms is now designated Griscelli syndrome type 1 or Elejalde disease. It has been attributed to pathogenic variants in the MYO5A gene, which affects melanosome transport.[116] Individuals with Griscelli syndrome type 2 have decreased cutaneous pigmentation and immunodeficiency but lack neurological deficits. They also may have hemophagocytosis or lymphohistiocytosis that is often fatal, like that seen in Chediak-Higashi syndrome. Griscelli syndrome type 2 is caused by pathogenic variants in RAB27A, which is part of the same melanosome transport pathway as MYO5A.[117] Griscelli syndrome type 3 presents with hypomelanosis and does not include neurologic or immunologic disorders. Pathogenic variants in the melanophilin (MLPH) gene and MYO5A have been associated with this variant of Griscelli syndrome.[118]

Epidermolysis bullosa

There are numerous forms of epidermolysis bullosa (EB), which is characterized by cleavage and blistering of the skin. Dystrophic EB and junctional EB are associated with an increased risk of skin cancer, particularly SCC.[119] The type of EB can be difficult to determine clinically, although genetic testing may aid in the classification. In one study of 91 probands with features of EB, a next-generation sequencing panel of 21 genes associated with different forms of EB or skin fragility syndromes was able to predict the subtype in 76 of 87 probands of undetermined subtype (83.5%).[120] Similar multigene panels are clinically available for EB. The types, pathogenic variants involved, and phenotypic characteristics are detailed in the following review.[121]
Dystrophic epidermolysis bullosa
Approximately 95% of individuals with the heritable disorder dystrophic epidermolysis bullosa (DEB) have a detectable germline pathogenic variant in the gene COL7A1. This gene, which is located at 3p21.3, is expressed in the basal keratinocytes of the epidermis and encodes for type VII collagen. This collagen forms a part of the fibrils that anchor the basement membrane to the dermis, thereby providing structural stability and resistance to mild skin trauma.[122] The lack of type VII collagen results in generalized blistering, often starting from birth, and is associated with skin atrophy and scarring.[122] A registry of DEB pathogenic variants, The International DEB Patient Registry, is accessible on the Internet.[123]
There are two recessively inherited subtypes of DEB: severe-generalized (RDEB-sev gen; previously named Hallopeau-Siemens type) and generalized-other or generalized-intermediate (RDEB-O; previously named non–Hallopeau-Siemens type); and a dominantly inherited form, dominant dystrophic epidermolysis bullosa (DDEB).[121] These syndromes are rare. The prevalence per million individuals in the United States and incidence per million live births are 0.36 and 0.57 for RDEB-sev gen, 0.14 and 0.30 for RDEB-O, and 1.49 and 2.12 for DDEB, respectively.[124] The clinical manifestations demonstrate a continuum of severity that complicates definitive diagnosis, especially early in life. The severe generalized subtype, associated with formation of pseudosyndactyly (a mitten-like deformity secondary to fusion of interdigital webbing) in early childhood, carries an SCC risk of up to 85% by age 45 years.[125,126] These cancers arise in nonhealing wounds and usually metastasize to cause death within 5 years of the diagnosis of SCC.[127] In one case series, SCC was the leading cause of death for the 15 patients with the severe generalized subtype.[128] The incidence of SCC appears to be highest in the RDEB subtype. In a review of 69 articles that included all types of EB, 117 individuals with SCC were identified; 81 of these cases (69.2%) were in individuals with RDEB.[119] In this group, the median age of diagnosis was 36 years (range, 6–71 y). Early mortality also has been observed in this disorder, with a mortality rate of up to 40% by age 30 years.[129] Extracutaneous manifestations of RDEB-sev gen include short stature, anemia, strictures of the gastrointestinal and genitourinary tracts, and corneal scarring that may result in blindness.
Diagnosis of EB may be accomplished by immunofluorescence or electron microscopy. A list of recommended diagnostic antibodies and their suppliers is available on the Dystrophic EB Research Association website. Pathogenic variant testing is generally used for prenatal diagnosis rather than for the primary diagnosis of EB.[130,131]
The rate of de novo pathogenic variants for DDEB is approximately 30%; maternal germline mosaicism has also been reported.[132,133] Glycine substitutions in exons 73 to 75 are the most common pathogenic variants in DDEB. G2034R and G2043R account for half of these variants. Less frequently, splice junction pathogenic variants and substitutions of glycine and other amino acids may cause the dominant form of DEB. In contrast, more than 400 pathogenic variants have been described for the two types of recessive EB. The recessive form of the disease is caused primarily by null variants, although amino acid substitutions, splice junction variants, and missense variants have also been reported. In-frame exon skipping may generate a partially functional protein in recessive disease. A founder pathogenic variant, c.6527insC (p.R525X), has been observed in 27 of 49 Spanish individuals with recessive DEB.[134] A founder pathogenic variant in COL7A1, pVal769LeuFsXI, was identified in 11 of 15 families in Sfax, Southern Tunisia.[135] Three of 12 individuals carrying at least one copy of this variant developed SCC, including two young-onset cases at ages 16 and 29 years. Genotype-phenotype correlations suggest an inverse correlation between the amount of functional protein and severity.
Pathogenic variants in COL7A1 result in abnormal triple helical coiling and decreased function, which causes increased skin fragility and blistering. In studies of Ras-driven carcinogenesis in RDEB-severe generalized keratinocytes, retention of the amino-terminal NC1, the first noncollagenous fragment of type VII collagen, is tumorigenic in mice.[136] This retained sequence may mediate tumor-stroma interactions that promote carcinogenesis.
Junctional epidermolysis bullosa
Junctional epidermolysis bullosa (JEB) is an autosomal recessive type of EB with an estimated prevalence of 0.49 per million individuals in the United States and an estimated incidence of 2.68 per million live births.[124] JEB results in considerable mortality, with approximately 50% of cases dying within the first year of life.[137] Pathogenic variants in any of the genes encoding the three basic subunits of laminin 332, previously known as laminin 5 (LAMA3LAMB3LAMC2), or variants in COL17A1 can result in this syndrome.[138-140] Individuals with the Herlitz type (a severe clinical form) of JEB are at increased risk of SCC, with a cumulative risk of 18% by age 25 years.[141] A study of COL17A1 in individuals with a milder subtype of JEB, called JEB-other, identified pathogenic variants in 85 of 86 alleles from 43 individuals.[142] Total loss of COL17A1 protein staining correlated with a more severe phenotype.

Epidermodysplasia verruciformis

Pathogenic variants in either of two adjacent genes on chromosome 17q25 can cause epidermodysplasia verruciformis, a rare heritable disorder associated with increased susceptibility to human papillomavirus (HPV). Infection with certain HPV subtypes can lead to development of generalized nonresolving verrucous lesions, which develop into in situand invasive SCCs in 30% to 60% of patients.[143] Malignant transformation is thought to occur in about half of these lesions. Approximately 90% of these lesions are attributed to HPV types 5 and 8,[144] although types 14, 17, 20, and 47 have occasionally been implicated. The association between HPV infection and increased risk of SCC has also been demonstrated in people without epidermodysplasia verruciformis; one case-control study found that HPV antibodies were found more frequently in the plasma of individuals with SCC (OR, 1.6; 95% CI, 1.2–2.3) than in plasma from cancer-free individuals.[145]
The genes associated with this disorder, EVER1 and EVER2, were identified in 2002.[146] The inheritance pattern of these genes appears to be autosomal recessive; however, autosomal dominant inheritance has also been reported.[147-149] Both of these gene products are transmembrane proteins localized to the endoplasmic reticulum, and they likely function in signal transduction. This effect may be through regulation of zinc balance; it has been shown that these proteins form a complex with the zinc transporter 1 (ZnT-1), which is, in turn, blocked by certain HPV proteins.[150]
A recent case-control study examined the effect of a specific EVER2 polymorphism(rs7208422) on the risk of cutaneous SCC in 239 individuals with prior SCC and 432 controls. This polymorphism is a (A > T) coding single nucleotide polymorphism in exon 8, codon 306 of the EVER2 gene. The frequency of the T allele among controls was 0.45. Homozygosityfor the polymorphism caused a modest increase in SCC risk, with an adjusted OR of 1.7 (95% CI, 1.1–2.7) relative to wild-type homozygotes. In this study, those with one or more of the T alleles were also found to have increased seropositivity for any HPV and for HPV types 5 and 8, as compared with the wild type.[151]
Some evidence suggests nonallelic heterogeneity in epidermodysplasia verruciformis. An individual born to consanguineous parents with epidermodysplasia verruciformis and additional bacterial and fungal infections was found to have homozygous R115X pathogenic variants in the MST1 gene.[152] Another susceptibility locus associated with this disorder has been identified at chromosome regions 2p21-p24 through linkage analysis of an affected consanguineous family. Unlike those with pathogenic variants in the EVER1 and EVER2 genes, affected individuals linked to this genomic region were infected with HPV 20 rather than the usual HPV subtypes associated with this disorder, and this family did not have a history of cutaneous SCC.[153]

Fanconi anemia

Fanconi anemia is a complex disorder that is characterized by increased incidence of hematologic and solid tumors, including SCC of the skin. Fanconi anemia is inherited as an autosomal recessive disease. It is a relatively rare syndrome with an estimated carrier frequency of one in 181 individuals in the United States (range: 1 in 156 to 1 in 209) and a carrier frequency of up to 1 in 100 individuals of Ashkenazi Jewish ancestry.[154] Leukemia is the most commonly reported cancer in this population, but increased rates of gastrointestinal, head and neck, and gynecologic cancers have also been seen.[155] By age 40 years, individuals affected with Fanconi anemia have an 8% risk per year of developing a solid tumor;[155] the median age of diagnosis for solid tumors is 26 years.[156] Multiple cases of cancers of the brain, breast, lung, and kidney (Wilms tumor) have been reported in this population.[156] Data on the incidence of NMSCs in this population are sparse; however, review of the literature suggests that the age of diagnosis is between the mid-20s and early 30s and that women seem to be affected more often than men.[156-160]
Individuals with this disease have increased susceptibility to DNA cross-linking agents (e.g., mitomycin-C or diepoxybutane) and ionizing and UV radiation. The diagnosis of this disease is made by observing increased chromosomal breakage, rearrangements, or exchanges in cells after exposure to carcinogens such as diepoxybutane.
Seventeen complementation groups have been identified for Fanconi anemia; details regarding the genes associated with these groups are listed in Table 7 below.[161] Exome sequencing has revealed that a subset of individuals can carry multiple heterozygous pathogenic variants in Fanconi anemia genes,[162] which may impact phenotypic presentation.
Table 7. Genes Associated with Fanconi Anemia (FA)
GeneLocusApproximate Incidence Among FA Patients (%)Pattern of Disease Transmission
AR = autosomal recessive; XLR = X-linked recessive.
FANCA16q24.370AR
FANCBXp22.31RareXLR
FANCC9q22.310AR
FANCD1 (BRCA2)13q12.3RareAR
FANCD23p25.3RareAR
FANCE6p21.310AR
FANCF11p15RareAR
FANCG (XRCC9)9p1310AR
FANCI (KIAA1794)15q25-26RareAR
FANCJ (BACH1/BRIP1)17q22.3RareAR
FANCL (PHF9/POG)2p16.1RareAR
FANCM (Hef)14q21.3RareAR
FANCN (PALB2)16p12.1RareAR
FANCO (RAD51C)17q22RareAR
FANCP (SLX4/BTBD12)16p13.3RareAR
FANCQ (ERCC4/XPF)16p13.12RareAR
FANCS (BRCA1)17q21.31RareAR
The proteins involved with DNA crosslink repairs have been termed the FANC pathway because of their involvement with Fanconi anemia.[163] They interact with several other proteins associated with hereditary cancer risk, including those for Bloom syndrome and ataxia-telangiectasia. Further investigation has revealed that FANCD1 is the same gene as BRCA2, a gene that causes predisposition to breast and ovarian cancer.[164] Other Fanconi anemia genes, FANCJ (BRIP1) and FANCN (PALB2), have also been identified as rare breast cancer susceptibility genes.[165] (Refer to the PDQ summary on Genetics of Breast and Gynecologic Cancers for more information about BRCA2BRIP1PALB2, and RAD51.) Individuals who are heterozygous carriers of other Fanconi anemia–associated variants do not appear to have an increased risk of cancer, with the possible exception of a twofold increase in breast cancer incidence in carriers of FANCC pathogenic variants.[166]
In 2018, a group reported a significant increase in SCC cases (OR, 1.69; 95% CI, 1.26–2.26) associated with a specific BRCA2 allele, which is relatively prevalent in the Icelandic population (K3326X; allele frequency, 1.1%).[167] This allele results in normal production of an altered protein, and the authors hypothesized carriers have an increased sensitivity to environmental factors, which require DNA repair. This variant was also associated with an increased risk of small cell lung cancer, breast cancer, and ovarian cancer (but lower than the risk associated with the BRCA pathogenic variants that decrease protein levels).

Dyskeratosis congenita (Zinsser-Cole-Engman syndrome)

Dyskeratosis congenita, like Werner syndrome, results in premature aging and is thus considered a progeroid disease. The classic clinical triad for diagnosis includes dysplastic nails, reticular pigmentation of the chest and neck, and oral leukoplakia. In addition, individuals with this disorder are at markedly increased risk of myelodysplastic syndrome, acute leukemia, and bone marrow failure. Ocular, dental, neurologic, gastrointestinal, pulmonary, and skeletal abnormalities have also been described in conjunction with this disease, but clinical expressivity is variable.[168] Developmental delay may also be present in variants of dyskeratosis congenita, such as Hoyeraal-Hreidarsson syndrome (HHS) and Revesz syndrome.
Approximately 10% of individuals with dyskeratosis congenita will develop nonhematologic tumors, often before the third decade of life.[169,170] Solid tumors may be the first manifestation of this disorder. Head and neck cancers were the most commonly reported, accounting for nearly half of the cancers observed. Cutaneous SCC occurred in about 1.5% of the subjects, and the median age at diagnosis was 21 years. These cancers are generally managed as any other SCC of the skin.
Several genes associated with telomere function (DKC1TERCTINF2NHP2NOP10RTEL1and TERT) have been implicated in dyskeratosis congenita; approximately one-half of the individuals with a clinical diagnosis of this disease have an identified pathogenic variant in one of these seven genes.[171-178TERC and TINF2 are inherited in an autosomal dominant manner, whereas NHP2 (NOLA2) and NOP10 (NOLA3) show autosomal recessive inheritance, and RTEL1 and TERT can be either autosomal dominant or autosomal recessive. Recessive pathogenic variants in RTEL1 can also be associated with HHS.[179] A study of more than 1,000 individuals of Ashkenazi Jewish ancestry identified a founder RTEL1 splice-site pathogenic variant, c.3791G>A (p.R1264H), that had a carrier frequency of 1% in Orthodox Ashkenazi Jewish individuals and 0.45% in the general Ashkenazi Jewish population.[180DKC1 shows an X-linked recessive pattern. Alterations in these genes result in shortening of telomeres, which in turn leads to defects in proliferation and spontaneous chromosomal rearrangements.[181] Levels of TERC, the RNA component of the telomerase complex, are reduced in all dyskeratosis congenita patients.[182] Missense pathogenic variants in WRAP53, a gene with a protein product that facilitates trafficking of telomerase, have also been associated with an autosomal recessive form of dyskeratosis congenita.[183] Pathogenic variants in C16orf57 were identified in 6 of 132 families who did not have a variant detected in other known genes.[184C16orf57 pathogenic variants are also associated with poikiloderma with neutropenia.[185] (Refer to the Rothmund-Thomson syndrome section of this summary for more information about poikiloderma congenitale.)
The recommended approach for diagnosis begins with a six-cell panel assay for leukocyte telomere length testing. If telomere length is in the lowest 1% for three or more cell types, molecular genetic testing is indicated.[186] Testing of DKC1 may be performed first in male probands, as pathogenic variants in this gene account for up to 36% of those identified in dyskeratosis congenita to date. Pathogenic variants in TINF2 and TERT are responsible for 11% to 24% and 6% to 10% of cases, respectively.[168,175,176,187,188]

Rothmund-Thomson syndrome

Rothmund-Thomson syndrome, also known as poikiloderma congenitale, is a heritable disorder characterized by chromosomal instability. The cutaneous presentation of this condition is an erythematous, blistering rash appearing on the face, buttocks, and extremities in early infancy. Other characteristics of this syndrome include telangiectasias, skeletal abnormalities, short stature, cataracts, and increased risk of osteosarcoma. Areas of hyperpigmentation and hypopigmentation of the skin develop later in life, and NMSCs can develop at an early age.[189] Reports of multiple SCCs in situ have been reported in individuals as young as 16 years.[190] The precise increased risk of skin cancer is not well characterized, but the point prevalence of NMSC, including both BCC and SCC, is 2% to 5% in young individuals affected by this syndrome.[191] This prevalence is clearly greater than that found in individuals in the same age group in the general population. Although increased UV sensitivity has been described, SCCs are also found in areas of the skin that are not exposed to the sun.[192]
A pathogenic variant in the gene RECQL4 is present in 66% of clinically affected individuals. This gene is located at 8q24.3, and inheritance is believed to be autosomal recessive.RECQL4 encodes the ATP-dependent DNA helicase Q4, which promotes DNA unwinding to allow for cellular processes such as replication, transcription, and repair. A role for this protein in repair of DNA double-strand breaks has also been suggested.[193] Pathogenic variants in similar DNA helicases lead to the inherited disorders of Bloom syndrome and Werner syndrome.
At least 19 different truncating pathogenic variants in this gene have been identified as deleterious.[194] These pathogenic variants cause severe down-regulation of RECQL4 transcripts in this subset of individuals with Rothmund-Thomson syndrome.[195] Cells deficient in RECQL4 have been found to be hypersensitive to oxidative stress, resulting in decreased DNA synthesis.[196] Deficiencies in the RecQ helicases permit hyper-recombination, thereby leading to loss of heterozygosity. Loss of heterozygosity associated with deficiencies of this protein suggests that the helicases are caretaker-type tumor suppressor proteins.[197]
Three of six families with Rothmund-Thomson syndrome were found to have homozygous pathogenic variants in the C16orf57 gene. Pathogenic variants in this gene have also been identified in individuals with dyskeratosis congenita and poikiloderma with neutropenia, suggesting that these syndromes are related;[184,185] however, skin cancer risk in these conditions is not well characterized. (Refer to the Dyskeratosis congenita [Zinsser-Cole-Engman syndrome] section of this summary for more information.)

Bloom syndrome

Loss of genomic stability is also the major cause of Bloom syndrome. This disorder shows increased chromosomal breakage and is diagnosed by increased sister chromatid exchanges on chromosomal analysis. Clinical manifestations of Bloom syndrome include severe growth retardation, recurrent infections, diabetes, chronic pulmonary disease, and an increased susceptibility to cancers of many types. The typical skin lesion seen in this disorder is a photosensitive erythematous telangiectatic rash that occurs in the first or second year of life. Although it is most commonly found on the face, it can also be present on the dorsa of hands or forearms. SCC of the skin is the third most common malignancy associated with this disorder. Skin cancer accounts for approximately 9% of tumors in the Bloom Syndrome Registry.[198] Skin cancers occur at an early age in this population, with a mean age of 31 years at the time of diagnosis.
The BLM gene, located on the short arm of chromosome 15, is the only gene known to be associated with Bloom syndrome. This gene encodes a 1,417-amino acid protein that is regulated by the cell cycle and demonstrates DNA-dependent ATPase and DNA duplex-unwinding activities. Its helicase domain shows considerable similarity to the RecQ subfamily of DNA helicases. Absence of this gene product is thought to destabilize other enzymes that participate in DNA replication and repair.[199,200]
This rare chromosomal breakage syndrome is inherited in an autosomal recessive manner and is characterized by loss of genomic stability. Sixty-four pathogenic variants described in the BLM gene include nucleotide insertions and deletions (41%), nonsense variants (30%), variants resulting in mis-splicing (14%), and missense variants (16%).[201,202] A specific pathogenic variant identified in the Ashkenazi Jewish population is a 6-bp deletion/7-bp insertion at nucleotide 2,281, designated as BLMASH.[203] Many of these variants result in truncation of the C-terminus, which prevents normal localization of this protein to the nucleus. Absence of functional BLM protein can cause increased rates of pathogenic variants and recombination. This somatic hypermutability leads to an increased risk of cancer at an early age in virtually every organ, including the skin.
Cells from people with Bloom syndrome have been found to have abnormal responses to UV radiation. Normal nuclear accumulation of TP53 after UV radiation was absent in 2 of 11 primary cultures from individuals with Bloom syndrome; in contrast, responses in cultures from people who have XP and ataxia-telangiectasia were normal.[204] The gene product of the BLM gene has also been found to complex with Fanconi proteins, raising the possibility of connections between the BLM and Fanconi anemia pathways for DNA stability.[205]

Werner syndrome

Like Bloom syndrome, Werner syndrome is characterized by spontaneous chromosomal instability, resulting in increased susceptibility to cancer and premature aging. Diagnostic criteria, often in the setting of consanguinity, include cataracts, short stature, premature graying or thinning of hair, and a positive 24-hour urinary hyaluronic acid test. Cardinal cutaneous manifestations of this disorder consist of sclerodermatous skin changes, ulcerations, atrophy, and pigmentation changes. Individuals with this syndrome have an average life expectancy of fewer than 50 years.[206] Cancers have an early onset and occur in up to 43% of these patients.[207] The spectrum of tumors associated with this disorder has primarily been described in the Japanese population and includes an increased incidence of sarcoma, thyroid cancers, and skin cancers.[208] Approximately 20% of the cancers reported in this syndrome are cutaneous, with melanoma and SCC of the skin accounting for 14% and 5%, respectively.[209] A study of 189 individuals with Werner syndrome estimated melanoma risk to be elevated 53-fold in these individuals.[210] SCC was less frequently diagnosed. Acral lentiginous melanomas are overrepresented, and SCCs may exhibit more aggressive behavior, with metastasis to lymph nodes and internal organs.[208,211]
Pathogenic variants in the WRN gene on chromosome 8p12-p11.2 have been identified in approximately 90% of individuals with this syndrome; no other genes are known to be associated with Werner syndrome.[207,212-215] Inheritance of this gene is believed to be autosomal recessive. The product of the WRN gene is a multifunctional protein including a DNA exonuclease and an ATP-dependent DNA helicase belonging to the RecQ subfamily. This protein may play a role in processes such as DNA repair, recombination, replication, transcription, and combined DNA functions.[216-224] Telomere dysfunction has been associated with premature aging and cancer susceptibility.[225] Other helicases with similar function are altered in other chromosomal instability syndromes, such as BLM in Bloom syndrome and RecQL4 in Rothmund-Thomson syndrome.
Pathogenic variants described in the WRN gene include all types of variants; however, the 1136C→T variant is the most common and is found in 20% to 25% of the Japanese and white populations.[226,227] In the Japanese population, a founder pathogenic variant (IVS 25-1G→C) is present in 60% of affected individuals.[228]
Pathogenic variants in the WRN gene causes loss of nuclear localization of the gene product. Intracellular levels of the mRNA and protein associated with the variant are also markedly decreased, compared with those of the wild type. Half-lives of the mRNA and protein associated with the variant are also shorter than those associated with the wild-type mRNA and protein.[227,229]

Interventions

Prevention and treatment of skin cancers

A phase III, double-blind, placebo-controlled clinical trial evaluated the effects of oral nicotinamide (vitamin B3) in 386 individuals with a history of at least two NMSCs within 5 years before study enrollment.[230] After 12 months of treatment, those taking nicotinamide 500 mg twice daily had a 30% reduction in the incidence of new SCCs (95% CI, 0%–51%; P = .05). A statistically significant reduction was also seen in actinic keratoses, the precursor skin lesions to SCCs. The rate of new NMSCs was 23% lower in the nicotinamide group (95% CI, 4–38, P = .02) than in the placebo group. No clinically significant differences in adverse events were observed between the two groups, and there was no evidence of benefit after discontinuation of nicotinamide. Of note, this study was not conducted in a population with an identified genetic predisposition to SCC.
Because many of the syndromes described above are rare, few clinical trials have been conducted in these specific populations. However, valuable information has been developed from the clinical management experience related to skin cancer risk and treatment in the XP population. Strict sun avoidance beginning in infancy, use of protective clothing, and close clinical monitoring of the skin are key components to management of XP. Full-body photography of the skin, conjunctivae, and eyelids is recommended to aid in follow-up.[231] Although few studies on treatment of SCC in the XP population have been done, in most cases treatment is similar to what would be recommended for the general population. Actinic keratoses are treated with topical therapies such as 5-fluorouracil (5-FU), cryotherapy with liquid nitrogen, or dermabrasion, whereas cutaneous cancers are generally managed surgically.[232]
Oral isotretinoin has been used as chemoprevention in XP patients with promising results. A small study of daily use of isotretinoin (13-cis retinoic acid; given as 2 mg/kg/day) reduced NMSC incidence by 63% in a small number of people with XP. Toxicities associated with this treatment included mucocutaneous symptoms, abnormalities in liver function tests and triglyceride levels, and musculoskeletal symptoms such as arthralgias, calcifications of tendons and ligaments, and osteoporosis.[233,234] Dose reduction to 0.5 mg/kg/day reduced toxicity and decreased skin cancer frequency in three of seven subjects (43%); increasing the dose to 1 mg/kg/day resulted in decreased skin cancer frequency in three of the four subjects who did not respond at the lower dose.[235] Oral isotretinoin use may be useful as a chemopreventive agent in other hereditary skin cancer syndromes, including basal cell nevus syndrome (BCNS), Rombo syndrome, EB, and epidermodysplasia verruciformis.[236,237]
Topical T4N5 liposome lotion, containing the bacterial enzyme T4 endonuclease V, was also investigated as a chemopreventive agent in a randomized, placebo-controlled trial of 30 XP patients.[238] Although no effect was seen on incidence of SCC, 17.7 fewer actinic keratoses per year were seen in the treatment group. Additionally, 1.6 fewer BCCs per year were observed in patients being treated with this therapy. Both of these results were statistically significant. The risk of BCC was reduced by 47%, which was of borderline statistical significance. No significant adverse effects of this agent were reported. To date, this agent has not been approved for use by the U.S. Food and Drug Administration.
For patients with XP and unresectable SCC, therapy with 5-FU has been investigated. Several treatment methods were used in this prospective study, including topical therapy to the lesions, short systemic infusion with folic acid, and continuous systemic infusion in combination with cisplatin. Topical 5-FU demonstrated some efficacy, but in some cases viable tumor remained in the deeper dermis. The systemic chemotherapy resulted in one complete response and three partial responses in a total of five patients, suggesting that this therapy may be an option for treatment of extensive lesions.[239] A dose reduction of 30% to 50% has been recommended for systemic chemotherapeutic agents in this population because of the increased sensitivity of XP cells.[240]
For patients with EB, wide local excision of SCC with 2 cm margins remains the treatment of choice. Amputation may be considered as an option to reduce disease recurrence, although it is not clear that this has an impact on survival. The role of sentinel lymph node biopsy remains unclear in this population.[237]
Current guidelines recommend that individuals with EB and unresectable SCC be treated with radiation therapy, but the dose may need to be given in smaller fractions in order to decrease the risk of skin desquamation. Systemic therapy with epidermal growth factor receptor antagonists or tyrosine kinase inhibitors may also be considered for individuals with advanced SCC.[237]
For people who have genetic disorders other than XP, data are lacking, but general sun-safety measures remain important. Careful protection of the skin and eyes is the mainstay of prevention in all patients with increased susceptibility to skin cancer. Key points include avoidance of sun exposure at peak hours, protective clothing and lenses, and vigilant use of sunscreen. Avoidance of x-ray therapy has also been advocated for some groups with hereditary skin cancer syndromes, such as those with epidermodysplasia verruciformis.[143] However, XP patients with unresectable skin cancers or internal cancers, such as spinal cord astrocytoma or glioblastomas of the brain, have been treated successfully with standard therapeutic doses of x-ray radiation.[48] Some experts recommend dermatologic evaluation every 6 months and ophthalmologic evaluation at least annually in these high-risk populations. Guidelines for the management of patients with EB recommend skin examinations every 3 to 6 months starting at age 10 years for individuals with the RDEB-sev gen subtype of the disease.[237] For individuals with other subtypes of EB, skin examination every 6 to 12 months starting at age 20 years is recommended in the absence of an established SCC diagnosis. Dental examination every 6 months is also recommended in this population.[237]
For individuals with DEB, wound care is paramount. Use of silver sulfadiazine cream, medical grade honey, and soft silicone dressings can be helpful in these settings. Attention to nutritional status, which may be compromised because of esophageal strictures, iron-deficiency anemia, infection, and inflammation, is another critical consideration for wound healing for these patients. Multivitamin supplementation, often at higher doses than those routinely recommended for the general population, may be warranted.[241]
Bone marrow transplantation has been explored in patients with DEB; however, there is no evidence that this intervention results in a reduction of skin cancer.[242] A double-blind, randomized, placebo-controlled trial of infusion of nonhematopoietic bone marrow stem cells with or without cyclosporine was conducted in 14 patients with recessive DEB. The rationale for this study was that mesenchymal stem cells (MSCs) have the potential to differentiate into dermal fibroblasts, the main expressor of type VII collagen. Seven subjects were randomly assigned to receive MSCs with 5 mg/kg/day of cyclosporine and an additional seven subjects received only MSCs. The number of new blisters and the rate of blister healing were significantly improved in both groups (P = .003 for the number of new blisters in the combination therapy group and P = .004 in the group receiving MSCs only; P< .001 for the rate of blister healing in both groups). However, no difference was seen between the groups.[243]

Future therapies for epidermolysis bullosa

Researchers are taking advantage of recent technological advances to study new strategies for the treatment of dominant and recessive EB.[244-247] Clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (Cas9) is a technology that can be used to edit DNA. One research group used CRISPR/Cas9 to correct an inherited pathogenic variant in COL7A1 in keratinocytes isolated from a patient with RDEB.[244] Keratinocytes that contained the corrected version of COL7A1 were successfully transplanted onto mice and staining of skin grafts after transplant showed normal skin. Another study used a different approach, retrovirus infection, to introduce normal COL7A1into keratinocytes from four RDEB patients.[246] The corrected keratinocytes were then assembled into epidermal graft sheets and transplanted onto six wound areas of each of the four patients. The grafts were well tolerated and showed greater healing capabilities than did noncorrected skin after further study. All of these therapies are still in early research stages and have not yet been evaluated in clinical trials.
Level of evidence: None assigned
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