Cutaneous phenotype and MC1R variants as modifying factors for the development of melanoma in CDKN2A G101W mutation carriers from 4 countries

Familial Melanoma and Susceptibility Genes: A Review of the Most Common Clinical and Dermoscopic Phenotypic Aspect, Associated Malignancies and Practical Tips for Management

A family history of melanoma greatly increases the risk of developing cutaneous melanoma, a highly aggressive skin cancer whose incidence has been steadily increasing worldwide. Familial melanomas account for about 10% of all malignant melanomas and display an inheritance pattern consistent with the presence of pathogenic germline mutations, among which those involving CDKN2A are the best characterized. In recent years, a growing number of genes, such as MC1R, MITF, CDK4, POT1, TERT, ACD, TERF2IP, and BAP1, have been implicated in familial melanoma. The fact that individuals harboring these germline mutations along with their close blood relatives have a higher risk of developing multiple primary melanomas as well as other internal organ malignancies, especially pancreatic cancer, makes cascade genetic testing and surveillance of these families of the utmost importance. Unfortunately, due to a polygenic inheritance mechanism involving multiple low-risk alleles, genetic modifiers, and environmental factors, it is still very difficult to predict the presence of these mutations. It is, however, known that germline mutation carriers can sometimes develop specific clinical traits, such as high atypical nevus counts and specific dermoscopic features, which could theoretically help clinicians predict the presence of these mutations in prone families. In this review, we provide a comprehensive overview of the high- and intermediate-penetrance genes primarily linked to familial melanoma, highlighting their most frequently associated non-cutaneous malignancies and clinical/dermoscopic phenotypes.

Dermoscopy comparative approach for early diagnosis in familial melanoma: influence of MC1R genotype

BACKGROUND

MC1R polymorphisms interact with CDKN2A mutations modulating melanoma risk and contribute to a less suspicious clinical and dermoscopic appearance of melanomas. Different strategies, including dermoscopic comparative approach and digital monitoring, are used for the melanoma diagnosis in this context.

OBJECTIVE

To analyse the diagnostic accuracy of the morphologic approach and comparative approach in dermoscopy, and to detect melanoma in familial melanoma (FamMM) patients according to different genetic backgrounds.

METHODS

Two independent readers evaluated 415 lesions belonging to 25 FamMM: 26 melanomas (62% in situ, 36% early invasive) and 389 naevi, blinded for dermoscopic and histopathologic diagnosis, following two different steps. First step-Randomized: all lesions were randomly located in one single folder. Second step-Comparative approach: the lesions were clustered by patient. Sensitivity, specificity and number needed to excise (NNE) for melanoma diagnosis were calculated for both diagnostic strategies. Sensitivity and specificity were also assessed regarding the genetic background.

RESULTS

The comparative approach showed lower sensitivity compared to the morphologic approach (69.2 and 73.1 vs. 76.9 both readers) but better specificity (95.9 and 95.1 vs. 84.3 and 90.2, respectively). NNE was better in the comparative approach. The readers had more difficulties diagnosing lesions from CDKN2A mutation carriers with red hair colour (RHC) MC1R variants.

CONCLUSION

The comparative approach can be useful in high-risk patients to decrease the NNE. Early melanomas in CDKN2A carriers with RHC polymorphisms are more difficult to diagnose even with the comparative approach and benefit from the detection of changes during digital dermoscopy monitoring for early diagnosis.

Clinical, pathological and dermoscopic phenotype of MITF p.E318K carrier cutaneous melanoma patients

BACKGROUND

The p.E318K variant of the Melanocyte Inducing Transcription Factor (MITF) has been implicated in genetic predisposition to melanoma as an intermediate penetrance allele. However, the impact of this variant on clinico-phenotypic, as well as on dermoscopic patterns features of affected patients is not entirely defined. The purpose of our study was to assess the association between the p.E318K germline variant and clinic-phenotypical features of MITF+ compared to non-carriers (MITF-), including dermoscopic findings of melanomas and dysplastic nevi.

METHODS

we retrospectively analyzed a consecutive series of 1386 patients recruited between 2000 and 2017 who underwent genetic testing for CDKN2A, CDK4, MC1R and MITF germline variants in our laboratory for diagnostic/research purposes. The patients were probands of melanoma-prone families and apparently sporadic single or multiple primary melanoma patients. For all, we collected clinical, pathological information and dermoscopic images of the histopathologically diagnosed melanomas and dysplastic nevi, when available.

RESULTS

After excluding patients positive for CDKN2A/CDK4 pathogenic variants and those affected by non-cutaneous melanomas, our study cohort comprised 984 cutaneous melanoma patients, 22 MITF+ and 962 MITF-. MITF+ were more likely to develop dysplastic nevi and multiple primary melanomas. Nodular melanoma was more common in MITF+ patients (32% compared to 19% in MITF-). MITF+ patients showed more frequently dysplastic nevi and melanomas with uncommon dermoscopic patterns (unspecific), as opposed to MITF- patients, whose most prevalent pattern was the multicomponent.

CONCLUSIONS

MITF+ patients tend to develop melanomas and dysplastic nevi with histopathological features, frequency and dermoscopic patterns often different from those prevalent in MITF- patients. Our results emphasize the importance of melanoma prevention programs for MITF+ patients, including dermatologic surveillance with digital follow-up.

CDKN2A germline mutations are not associated with poor survival in an Italian cohort of melanoma patients

BACKGROUND

Cyclin dependent kinase inhibitor 2A gene (CDKN2A) germline mutations have recently been associated with poor survival in patients with melanoma. Despite the high mutation rate in our cohort (up to 10% in patients with apparently sporadic melanoma), information on the impact of CDKN2A on survival in this cohort is lacking.

OBJECTIVE

To investigate whether poor survival associated with CDKN2A germline mutations was confirmed in a high mutation-prevalence cohort of Italian patients with melanoma undergoing a mutation-based follow-up.

METHODS

A total of 1239 patients with cutaneous melanoma were tested for CDKN2A mutational status and then assigned to a follow-up scheme according not only to family history but also to CDKN2A mutational status, as follow-up intervals were more frequent for CDKN2A germline mutation-positive (MUT⁺) patients. From this cohort, we selected 106 MUT⁺ patients (with familial melanoma or apparently sporadic melanoma) and 199 CDKN2A germline mutation-negative (MUT^-) patients with sporadic melanoma who were matched by age and sex and had a similar tumor stage distribution.

RESULTS

We found no difference in overall survival (hazard ratio, 0.85; 95% confidence interval, 0.48-1.52; P = .592,) or melanoma-specific survival (hazard ratio, 0.86; 95% confidence interval, 0.38-1.95; P = .718,) between MUT⁺ and MUT^- patients. MUT⁺ patients were more likely to develop multiple melanomas and to undergo surgical excision of dysplastic nevi than were MUT^- patients.

LIMITATIONS

Retrospective study.

CONCLUSION

CDKN2A mutations were not associated with survival in our cohort.

Genetic susceptibility to cutaneous melanoma in southern Switzerland: role of CDKN2A, MC1R and MITF

BACKGROUND

Nearly 10% of all cases of cutaneous melanoma (CM) occur in patients with a personal or family history of the disease.

OBJECTIVES

To obtain information about genetic predisposition to CM in Ticino, the southern region of Switzerland, a zone with moderate-to-high CM incidence.

METHODS

We identified germline mutations in highly CM-associated genes (CDKN2A and CDK4) and low/medium-penetrance variants (MC1R and MITF) in patients with multiple primary CMs or individuals with one or more CM and a positive family history for CM or pancreatic cancer among first- or second-degree relatives. Healthy blood donors (n = 146) were included as a control group.

RESULTS

From July 2010 to July 2012, 57 patients (41 pedigrees) were included. Twenty-six were melanoma-prone families (with at least two cases) and 15 had multiple CMs. Pancreatic cancer was found in six families. The CDKN2A mutation p.V126D was identified in seven patients (four families) with a founder effect, whereas CDKN2A A148T was detected in seven cases (five families) and seven healthy donors (odds ratio 2·76, 95% confidence interval 0·83-9·20). At least one MC1R melanoma-associated polymorphism was detected in 32 patients (78%) and 97 healthy donors (66%), with more than one polymorphism in 12 patients (29%) and 25 healthy donors (17%). The MITF variant p.E318K was identified in four patients from three additional pedigrees (7%) and one healthy control (0·7%).

CONCLUSIONS

Inclusion criteria for the Ticino population for genetic assessment should follow the rule of two (two affected individuals in a family or a patient with multiple CMs), as we detected a CDKN2A mutation in almost 10% of our pedigrees (four of 41), MITF p.E318K in 7% (three of 41) and a higher number of MC1R variants than in the control population.

Pigmentary Markers in Danes--Associations with Quantitative Skin Colour, Nevi Count, Familial Atypical Multiple-Mole, and Melanoma Syndrome

To investigate whether pigmentation genes involved in the melanogenic pathway (melanogenesis) contributed to melanoma predisposition, we compared pigmentary genetics with quantitative skin pigmentation measurements, the number of atypical nevi, the total nevus count, and the familial atypical multiple mole and melanoma (FAMMM) syndrome. We typed 32 pigmentary SNP markers and sequenced MC1R in 246 healthy individuals and 116 individuals attending periodic control for malignant melanoma development, 50 of which were diagnosed with FAMMM. It was observed that individuals with any two grouped MC1R variants (missense, NM_002386:c. 456C > A (p.TYR152*), or NM_002386:c.83_84insA (p.Asn29Glnfs*14) had significantly (p<0.001) lighter skin pigmentation of the upper-inner arm than those with none or one MC1R variant. We did not observe any significant association of the MC1R variants with constitutive pigmentation measured on the buttock area. We hypothesize that the effect of MC1R variants on arm pigmentation is primarily reflecting the inability to tan when subjected to UVR. A gender specific effect on skin pigmentation was also observed, and it was found that the skin pigmentation of females on average were darker than that of males (p<0.01). We conclude that MC1R variants are associated with quantitative skin colour in a lightly pigmented Danish population. We did not observe any association between any pigmentary marker and the FAMMM syndrome. We suggest that the genetics of FAMMM is not related to the genetics of the pigmentary pathway.

Epidemiological and genetic factors underlying melanoma development in Italy

Among human cancers, melanoma remains one of the malignancies with an ever-growing incidence in white populations. Recent advances in biological and immunological therapeutic approaches as well as increased efforts for secondary prevention are contributing to improve the survival rates. It is likely that a significant fall in mortality rates for melanoma will be achieved by further increase of the early detection through a more accurate selection of the higher-risk individuals (i.e., carriers of predisposing genetic alterations). A similar scenario occurs in Italy. In the present review, we have considered data on incidence, survival and mortality rates of melanoma in Italian population, including evaluation of the main risk factors and genetic mutations underlying disease susceptibility.

Sporadic melanoma in South-Eastern Italy: the impact of melanocortin 1 receptor (MC1R) polymorphism analysis in low-risk people and report of three novel variants

Environmental and genetic risk factors are involved in the development of melanoma. The role of the melanocortin 1 receptor (MC1R) gene has been investigated and differences according to geographic areas have been described. To evaluate the role of some clinical and genetic risk factors in melanoma development, we performed a case-control study involving 101 melanoma patients and 103 controls coming from South-Eastern Italy (Puglia), after achieving informed consent. We confirmed the role of known clinical risk factors for melanoma. Furthermore, 42 MC1R polymorphisms were observed. Three of these variants (L26V, H232L, D294Y) were not previously reported in the literature. Their predicted impact on receptor function was evaluated using bioinformatic tools. We report an overall frequency of MC1R variants in our population higher than in Northern or Central Italy. The most common polymorphism found was V60L, that has been recently reported to spread among South Mediterranean population. This variant influenced phenotypic characteristics of our population while it did not impinge on melanoma risk. An increased risk of melanoma was associated with two or more MC1R variants, when at least one was RHC, compared to people carrying the MC1R consensus sequence or a single MC1R polymorphism. Interestingly, we observed an increased risk of melanoma in subjects with darker skin and lower nevus count, usually considered at low risk, when carrying MC1R polymorphisms.

CDKN2A unclassified variants in familial malignant melanoma: combining functional and computational approaches for their assessment

CDKN2A codes for two oncosuppressors by alternative splicing of two first exons: p16INK4a and p14ARF. Germline mutations are found in about 40% of melanoma-prone families, and most of them are missense mutations mainly affecting p16INK4a. A growing number of p16INK4a variants of uncertain significance (VUS) are being identified but, unless their pathogenic role can be demonstrated, they cannot be used for identification of carriers at risk. Predicting the effect of these VUS by either a "standard" in silico approach, or functional tests alone, is rather difficult. Here, we report a protocol for the assessment of any p16INK4a VUS, which combines experimental and computational tools in an integrated approach. We analyzed p16INK4a VUS from melanoma patients as well as variants derived through permutation of conserved p16INK4a amino acids. Variants were expressed in a p16INK4a-null cell line (U2-OS) and tested for their ability to block proliferation. In parallel, these VUS underwent in silico prediction analysis and molecular dynamics simulations. Evaluation of in silico and functional data disclosed a high agreement for 15/16 missense mutations, suggesting that this approach could represent a pilot study for the definition of a protocol applicable to VUS in general, involved in other diseases, as well.

A large de novo 9p21.3 deletion in a girl affected by astrocytoma and multiple melanoma

Background

Association of melanoma, neural system tumors and germ line mutations at the 9p21 region in the CDKN2A, CDKN2B and CDKN2BAS genes has been reported in a small number of families worldwide and described as a discrete syndrome in melanoma families registered as a rare disease, the melanoma–astrocytoma syndrome.

Case presentation

We here studied two young patients developing melanoma after radiotherapy for astrocytoma, both reporting lack of family history for melanoma or neural system tumors at genetic counselling. Patient A is a girl treated for anaplastic astrocytoma at 10 years and for multiple melanomas on the scalp associated to dysplastic nevi two years later. Her monozygotic twin sister carried dysplastic nevi and a slow growing, untreated cerebral lesion. Direct sequencing analysis showed no alterations in melanoma susceptibility genes including CDKN2A, CDK4, MC1R and MITF or in TP53. By microsatellite analysis, multiplex ligation-dependent probe amplification, and array comparative genomic hybridization a deletion including the CDKN2A, CDKN2B and CDKN2BAS gene cluster was detected in both twin sisters, encompassing a large region at 9p21.3 and occurring de novo after the loss of one paternal allele.

Patient B is a boy of 7 years when treated for astrocytoma then developing melanoma associated to congenital nevi on the head 10 years later: sequencing and multiplex ligation-dependent probe amplification revealed a normal profile of the CDKN2A/CDKN2B/CDKN2BAS region. Array comparative genomic hybridization confirmed the absence of deletions at 9p21.3 and failed to reveal known pathogenic copy number variations.

Conclusions

By comparison with the other germ line deletions at the CDKN2A, CDKN2B and CDKN2BAS gene cluster reported in melanoma susceptible families, the deletion detected in the two sisters is peculiar for its de novo origin and for its extension, as it represents the largest constitutive deletion at 9p21.3 region identified so far.

In addition, the two studied cases add to other evidence indicating association of melanoma with exposure to ionizing radiation and with second neoplasm after childhood cancer. Melanoma should be considered in the monitoring of pigmented lesions in young cancer patients.

Capturing the biological impact of CDKN2A and MC1R genes as an early predisposing event in melanoma and non melanoma skin cancer

Germline mutations in CDKN2A and/or red hair color variants in MC1R genes are associated with an increased susceptibility to develop cutaneous melanoma or non melanoma skin cancer. We studied the impact of the CDKN2A germinal mutation p.G101W and MC1R variants on gene expression and transcription profiles associated with skin cancer. To this end we set-up primary skin cell co-cultures from siblings of melanoma prone-families that were later analyzed using the expression array approach. As a result, we found that 1535 transcripts were deregulated in CDKN2A mutated cells, with over-expression of immunity-related genes (HLA-DPB1, CLEC2B, IFI44, IFI44L, IFI27, IFIT1, IFIT2, SP110 and IFNK) and down-regulation of genes playing a role in the Notch signaling pathway. 3570 transcripts were deregulated in MC1R variant carriers. In particular, genes related to oxidative stress and DNA damage pathways were up-regulated as well as genes associated with neurodegenerative diseases such as Parkinson's, Alzheimer and Huntington. Finally, we observed that the expression signatures indentified in phenotypically normal cells carrying CDKN2A mutations or MC1R variants are maintained in skin cancer tumors (melanoma and squamous cell carcinoma). These results indicate that transcriptome deregulation represents an early event critical for skin cancer development.

CDKN2A and MC1R variants influence dermoscopic and confocal features of benign melanocytic lesions in multiple melanoma patients

Non-invasive diagnostic tools are effective in the histomorphological study of melanocytic lesions. The role of melanoma susceptibility genes on melanocytic nevi histopathological features is not clear. The current study aimed to correlate genetic alterations and histomorphological features of melanocytic nevi. Clinical, dermoscopic and confocal features of 34 multiple melanoma patients and 34 controls were compared. Among patients with melanoma, carriers of CDKN2A mutations and/or MC1R variants, and wild-type genes were also compared. In patients with melanoma, a lighter phototype (P = 0.051), a higher number of nevi (P < 0.01) and clinically atypical nevi (P < 0.01) were observed. At dermoscopy, these nevi showed a complex pattern (P = 0.011), atypical network (P = 0.018) and irregular pigmentation (P = 0.037); at confocal, an irregular meshwork pattern (P = 0.026) with atypical nests (P = 0.016) and an inflammatory infiltrate (P = 0.048) were observed. Among patients with melanoma genetically tested, CDKN2A G101W mutation carriers were more frequently younger (P = 0.023), with clinically atypical nevi (P = 0.050), with cytological atypia (P = 0.033) at confocal. G101W mutation and MC1R variants carriers showed hypopigmented nevi (P = 0.002) and, at confocal, roundish cells infiltrating the junction (P = 0.019). These data suggest an influence of CDKN2A mutation and MC1R variants in the development of dysplastic melanocytic lesions. Non-invasive histomorphological evaluation, together with genetic studies, improves melanoma risk identification and early diagnosis, for a patient-tailored management.

MC1R variation and melanoma risk in relation to host/clinical and environmental factors in CDKN2A positive and negative melanoma patients

Host, environmental and genetic factors differently modulate cutaneous melanoma (CM) risk across populations. Currently, the main genetic risk determinants are germline mutations in the major known high-risk susceptibility genes, CDKN2A and CDK4, and variants of the low-risk gene MC1R, which is key in the pigmentation process. This case-control study aimed at investigating the influence of the main host and environmental risk factors and of MC1R variation on CM risk in 390 CDKN2A-negative and 49 CDKN2A-positive Italian individuals. Multivariate analysis showed that MC1R variation, number of nevi and childhood sunburns doubled CM risk in CDKN2A-negative individuals. In CDKN2A-positive individuals, family history of CM and presence of atypical nevi, rather than MC1R status, modified risk (20.75- and 2.83-fold, respectively). Occupational sun exposure increased CM risk (three to sixfold) in both CDKN2A-negative and CDKN2A-positive individuals, reflecting the occupational habits of the Ligurian population and the geographical position of Liguria.

Melanoma prone families with CDK4 germline mutation: phenotypic profile and associations with MC1R variants

Background

CDKN2A and CDK4 are high risk susceptibility genes for cutaneous malignant melanoma. Melanoma families with CDKN2A germline mutations have been extensively characterised, whereas CDK4 families are rare and lack a systematic investigation of their phenotype.

Methods

All known families with CDK4 germline mutations (n=17) were recruited for the study by contacting the authors of published papers or by requests via the Melanoma Genetics Consortium (GenoMEL). Phenotypic data related to primary melanoma and pigmentation characteristics were collected. The CDK4 exon 2 and the complete coding region of the MC1R gene were sequenced.

Results

Eleven families carried the CDK4 R24H mutation whereas six families had the R24C mutation. The total number of subjects with verified melanoma was 103, with a median age at first melanoma diagnosis of 39 years. Forty-three (41.7%) subjects had developed multiple primary melanomas (MPM). A CDK4 mutation was found in 89 (including 62 melanoma cases) of 209 tested subjects. CDK4 positive family members (both melanoma cases and unaffected subjects) were more likely to have clinically atypical nevi than CDK4 negative family members (p<0.001). MPM subjects had a higher frequency of MC1R red hair colour variants compared with subjects with one tumour (p=0.010).

Conclusion

Our study shows that families with CDK4 germline mutations cannot be distinguished phenotypically from CDKN2A melanoma families, which are characterised by early onset of disease, increased occurrence of clinically atypical nevi, and development of MPM. In a clinical setting, the CDK4 gene should therefore always be examined when a melanoma family tests negative for CDKN2A mutation.

Inherited variants in the MC1R gene and survival from cutaneous melanoma: a BioGenoMEL study

Inherited MC1R variants modulate MITF transcription factor signaling, which in turn affects tumor cell proliferation, apoptosis, and DNA repair. The aim of this BioGenoMEL collaborative study in 10 melanoma cohorts was to test the hypothesis that inherited variants thereby moderate survival expectation. A survival analysis in the largest cohort (Leeds) was carried out adjusting for factors known to impact on survival. The results were then compared with data from nine smaller cohorts. The absence of any consensus MC1R alleles was associated with a significantly lower risk of death in the Leeds set (HR, 0.64; 95% CI, 0.46–0.89) and overall in the 10 data sets (HR, 0.78; 95% CI, 0.65–0.94) with some support from the nine smaller data sets considered together (HR, 0.83; 95% CI, 0.67–1.04). The data are suggestive of a survival benefit for inherited MC1R variants in melanoma patients.

Association of MC1R variants and host phenotypes with melanoma risk in CDKN2A mutation carriers: a GenoMEL study

Background

Carrying the cyclin-dependent kinase inhibitor 2A (CDKN2A) germline mutations is associated with a high risk for melanoma. Penetrance of CDKN2A mutations is modified by pigmentation characteristics, nevus phenotypes, and some variants of the melanocortin-1 receptor gene (MC1R), which is known to have a role in the pigmentation process. However, investigation of the associations of both MC1R variants and host phenotypes with melanoma risk has been limited.

Methods

We included 815 CDKN2A mutation carriers (473 affected, and 342 unaffected, with melanoma) from 186 families from 15 centers in Europe, North America, and Australia who participated in the Melanoma Genetics Consortium. In this family-based study, we assessed the associations of the four most frequent MC1R variants (V60L, V92M, R151C, and R160W) and the number of variants (1, ≥2 variants), alone or jointly with the host phenotypes (hair color, propensity to sunburn, and number of nevi), with melanoma risk in CDKN2A mutation carriers. These associations were estimated and tested using generalized estimating equations. All statistical tests were two-sided.

Results

Carrying any one of the four most frequent MC1R variants (V60L, V92M, R151C, R160W) in CDKN2A mutation carriers was associated with a statistically significantly increased risk for melanoma across all continents (1.24 × 10⁻⁶ ≤ P ≤ .0007). A consistent pattern of increase in melanoma risk was also associated with increase in number of MC1R variants. The risk of melanoma associated with at least two MC1R variants was 2.6-fold higher than the risk associated with only one variant (odds ratio = 5.83 [95% confidence interval = 3.60 to 9.46] vs 2.25 [95% confidence interval = 1.44 to 3.52]; P_trend = 1.86 × 10⁻⁸). The joint analysis of MC1R variants and host phenotypes showed statistically significant associations of melanoma risk, together with MC1R variants (.0001 ≤ P ≤ .04), hair color (.006 ≤ P ≤ .06), and number of nevi (6.9 × 10⁻⁶ ≤ P ≤ .02).

Conclusion

Results show that MC1R variants, hair color, and number of nevi were jointly associated with melanoma risk in CDKN2A mutation carriers. This joint association may have important consequences for risk assessments in familial settings.

Genetics of pigmentation in skin cancer--a review

Skin pigmentation is one of the most overt human physical traits with consequences on susceptibility to skin cancer. The variations in skin pigmentation are dependent on geographic location and population ethnicity. Skin colouration is mainly due to the pigmentation substance melanin, produced in specialized organelles (melanosomes) within dendritic melanocytes, and transferred to neighbouring keratinocytes. The two types of melanin synthesized in well defined chemical reactions are the protective dark coloured eumelanin and the sulphur containing light red-yellow pheomelanin. The events leading to the synthesis of melanin are controlled by signalling cascades that involve a host of genes encoding ligands, receptors, transcription factors, channel transporters and many other crucial molecules. Several variants within the genes involved in pigmentation have been associated with high risk phenotypes like fair skin, brown-red hair and green-blue eyes. Many of those variants have also been implicated in the risk of various skin cancers. The variants within the key pigmentation gene, melanocortin-receptor 1 (MC1R), in particular have been ubiquitously linked with high risk traits and skin cancers involving both pigmentary and non-pigmentary functions and likely interaction with variants in other genes. Many of the variants in other genes, functional in pigmentation pathway, have also been associated with phenotypic variation and risk of skin cancers. Those genes include agouti signalling protein (ASIP), tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), oculocutaneous albinism II (OCA2), various solute carrier genes and transporters. Most of those associations have been confirmed in genome wide association studies that at the same time have also identified new loci involved in phenotypic variation and skin cancer risk. In conclusion, the genetic variants within the genes involved in skin pigmentation besides influencing phenotypic traits are important determinants of risk of several skin cancers. However, ultimate risk of skin cancer is dependent on interplay between genetic and host factors.

Selection criteria for genetic assessment of patients with familial melanoma

Approximately 5% to 10% of melanoma may be hereditary in nature, and about 2% of melanoma can be specifically attributed to pathogenic germline mutations in cyclin-dependent kinase inhibitor 2A (CDKN2A). To appropriately identify the small proportion of patients who benefit most from referral to a genetics specialist for consideration of genetic testing for CDKN2A, we have reviewed available published studies of CDKN2A mutation analysis in cohorts with invasive, cutaneous melanoma and found variability in the rate of CDKN2A mutations based on geography, ethnicity, and the type of study and eligibility criteria used. Except in regions of high melanoma incidence, such as Australia, we found higher rates of CDKN2A positivity in individuals with 3 or more primary invasive melanomas and/or families with at least one invasive melanoma and two or more other diagnoses of invasive melanoma and/or pancreatic cancer among first- or second-degree relatives on the same side of the family. The work summarized in this review should help identify individuals who are appropriate candidates for referral for genetic consultation and possible testing.

The melanocortin-1 receptor gene polymorphism and association with human skin cancer

The melanocortin-1 receptor (MC1R) is a key gene involved in the regulation of melanin synthesis and encodes a G-protein coupled receptor expressed on the surface of the melanocyte in the skin and hair follicles. MC1R activation after ultraviolet radiation exposure results in the production of the dark eumelanin pigment and the tanning process in humans, providing physical protection against DNA damage. The MC1R gene is highly polymorphic in Caucasian populations with a number of MC1R variant alleles associated with red hair, fair skin, freckling, poor tanning, and increased risk of melanoma and nonmelanoma skin cancer. Variant receptors have shown alterations in biochemical function, largely due to intracellular retention or impaired G-protein coupling, but retain some signaling ability. The association of MC1R variant alleles with skin cancer risk remains after correction for pigmentation phenotype, indicating regulation of nonpigmentary pathways. Notably, MC1R activation has been linked to DNA repair and may also contribute to the regulation of immune responses.

Melanoma epidemiology

Melanoma is a complex, heterogeneous cancer that continues to increase in incidence. Multiple studies have consistently identified major host and environmental risk factors for melanoma. Nevi, particularly dysplastic nevi, confer much higher risks than most pigmentary characteristics. Ultraviolet radiation exposure is the predominant environmental risk factor for melanoma. Recently, both rare high risk susceptibility genes and common polymorphic genes contributing to melanoma risk have been identified.

CDKN2A mutations in melanoma families from Uruguay

BACKGROUND

Familial melanoma, a cluster of several cases within a single family, accounts for approximately 10% of cases of melanoma. Hereditary melanoma is defined as two or more first-degree relatives having melanoma. A member of a melanoma-prone family has a 35-70-fold increased relative risk of developing a melanoma. Genetic susceptibility is linked to the major susceptibility genes CDKN2A and CDK4, and the minor susceptibility gene MC1R.

OBJECTIVES

To determine the clinical and genetic characteristics of cutaneous melanoma in melanoma-prone families from Uruguay.

METHODS

We studied 13 individuals from six melanoma-prone families living in Uruguay. Phenotype, familial and personal history were recorded. Molecular screening of CDKN2A and CDK4 was done by polymerase chain reaction-single strand conformational polymorphism analysis. The MC1R gene was sequenced.

RESULTS

Mutations in CDKN2A were detected in five of six families: c.-34G>T, p.G101W and p.E88X. A novel germline mutation p.E88X, associated with hereditary melanoma in two unrelated families, is described. We hypothesize that a founder effect occurred probably in the Mediterranean region. No mutations in CDK4 were detected. Six different MC1R variants, all previously reported, were present in Uruguayan families.

CONCLUSIONS

The overall rate of deleterious CDKN2A mutations in our familial melanoma pedigrees, even though the sample size is small, was considerably higher (83%) than the often quoted range.

Management of familial melanoma and nonmelanoma skin cancer syndromes

The clinical manifestations of hereditary skin cancer syndromes depend upon the interplay between environmental and genetic factors. Familial melanoma occurs in the setting of hereditary susceptibility, with a complex phenotype of early age of onset, multiple atypical moles, multiple primary melanomas, multiple melanomas in the family, and in some instances pancreatic cancer. Identification of individuals who may have a hereditary susceptibility for the development of melanoma is essential to provide an opportunity for primary prevention, and to target high-risk groups for early diagnosis and treatment. Consequently, the surgeon as one of the primary caregivers should be familiar with hereditary skin cancer syndromes and their pathogenesis, diagnosis, management, and surveillance recommendations. This article discusses a practical approach for some of the issues likely encountered by the surgeon in the management of familial melanoma and non-melanoma skin cancer.

The contribution of large genomic deletions at the CDKN2A locus to the burden of familial melanoma

Mutations in two genes encoding cell cycle regulatory proteins have been shown to cause familial cutaneous malignant melanoma (CMM). About 20% of melanoma-prone families bear a point mutation in the CDKN2A locus at 9p21, which encodes two unrelated proteins, p16^INK4a and p14^ARF. Rare mutations in CDK4 have also been linked to the disease. Although the CDKN2A gene has been shown to be the major melanoma predisposing gene, there remains a significant proportion of melanoma kindreds linked to 9p21 in which germline mutations of CDKN2A have not been identified through direct exon sequencing. The purpose of this study was to assess the contribution of large rearrangements in CDKN2A to the disease in melanoma-prone families using multiplex ligation-dependent probe amplification. We examined 214 patients from independent pedigrees with at least two CMM cases. All had been tested for CDKN2A and CDK4 point mutation, and 47 were found positive. Among the remaining 167 negative patients, one carried a novel genomic deletion of CDKN2A exon 2. Overall, genomic deletions represented 2.1% of total mutations in this series (1 of 48), confirming that they explain a very small proportion of CMM susceptibility. In addition, we excluded a new gene on 9p21, KLHL9, as being a major CMM gene.