Improvement of Genetic Testing for Cutaneous Melanoma in Countries With Low to Moderate Incidence: The Rule of 2 vs the Rule of 3

Germline cancer susceptibility in individuals with melanoma

BACKGROUND

Prior studies have estimated a small number of individuals with melanoma (2%-2.5%) have germline cancer predisposition, yet a recent twin study suggested melanoma has the highest hereditability among cancers.

OBJECTIVE

To determine the incidence of hereditary melanoma and characterize the spectrum of cancer predisposition genes that may increase the risk of melanoma.

METHODS

Four hundred individuals with melanoma and personal or family history of cancers underwent germline testing of >80 cancer predisposition genes. Comparative analysis of germline data was performed on 3 additional oncologic and dermatologic data sets.

RESULTS

Germline pathogenic/likely pathogenic (P/LP) variants were identified in 15.3% (61) individuals with melanoma. Most variants (41, 67%) involved genes considered unrelated to melanoma (BLM, BRIP1, CHEK2, MLH1, MSH2, PMS2, RAD51C). A third (20, 33%) were in genes previously associated with familial melanoma (BAP1, BRCA2, CDKN2A, MITF, TP53). Nearly half (30, 46.9%) of P/LP variants were in homologous repair deficiency genes. Validation cohorts demonstrated P/LP rates of 10.6% from an unselected oncologic cohort, 15.8% from a selected commercial testing cohort, and 14.5% from a highly selected dermatologic study.

LIMITATIONS

Cohorts with varying degrees of selection, some retrospective.

CONCLUSION

Germline predisposition in individuals with melanoma is common, with clinically actionable findings diagnosed in 10.6% to 15.8%.

Multiple Primary Melanoma: A Five-Year Prospective Single-Center Follow-Up Study of Two MC1R R/R Genotype Carriers

BACKGROUND

Multiple primary melanoma (MPM) is a diagnostic challenge even with ancillary imaging technologies available to dermatologists. In selected patients' phenotypes, the use of imaging approaches can help better understand lesion characteristics, and aid in early diagnosis and management.

METHODS

Under a 5-year prospective single-center follow-up, 58 s primary melanomas (SPMs) were diagnosed in two first-degree relatives, with fair skin color, red hair, green eyes, and personal history of one previous melanoma each. Patients' behavior and descriptive demographic data were collected from medical records. The information on the first two primary melanomas (PMs) were retrieved from pathology reports. The characteristics of 60 melanomas were collected from medical records, video dermoscopy software, and pathology reports. Reflectance confocal microscopy (RCM) was performed prior to excision of 22 randomly selected melanomas.

RESULTS

From February 2018 to May 2023, two patients underwent a pooled total of 214 excisional biopsies of suspect lesions, resulting in a combined benign versus malignant treatment ratio (NNT) of 2.0:1.0. The number of moles excised for each melanoma diagnosed (NNE) was 1.7:1.0 and 6.9:1.0 for the female and male patient respectively. The in-situ melanoma/invasive melanoma ratio (IIR) demonstrated a higher proportion of in-situ melanomas for both patients. From June 2018 to May 2023, a total of 58 SPMs were detected by the combination of total body skin exam (TBSE), total body skin photography (TBSP), digital dermoscopy (DD), and sequential digital dermoscopy imaging (SDDI) via comparative approach. The younger patient had her PM one month prior to the second and third cutaneous melanomas (CMs), characterizing a case of synchronous primary CM. The male older relative had a total of 7 nonsynchronous melanomas.

CONCLUSIONS

This CM cohort is composed of 83.3% in-situ melanoma and 16.7% invasive melanoma. Both patients had a higher percentage of SPM with clinical nevus-like morphology (84.5%), global dermoscopic pattern of asymmetric multiple component (60.3%) and located on the lower limbs (46.6%). When RCM was performed prior to excision, 81% of SPM had features suggestive of malignancy. As well, invasive melanomas were more frequent in the lower limbs (40%). In the multivariate model, for the two high-risk patients studied, the chance of a not associated with nevus ("de novo") invasive SPM diagnosis is 25 times greater than the chance of a diagnosis of a nevus-associated invasive SPM.

Targeted germline sequencing of patients with three or more primary melanomas reveals high rate of pathogenic variants

Individuals with multiple primary melanomas have rates of germline CDKN2A pathogenic variants of 3%-18%, and are also frequent carriers of variants in the melanocortin-1 receptor. Few patients with numerous (≥3) primary melanomas have been studied with respect to these or other potential germline pathogenic variants. We investigated 46 patients with ≥3 primary melanomas (3, n = 17; 4, n = 14; 5-14, n = 15) to determine if higher rates of germline pathogenic variants of CDKN2A, MC1R, or other cancer genes could explain their extreme melanoma phenotype. Most (43/46, 93%) patients had variants in MC1R and 11/46 (24%) had CDKN2A pathogenic variants, but only male sex and having two variants in MC1R correlated with increasing number of melanomas. Panel screening of 56 other cancer predisposition genes did not reveal other germline pathogenic variants associated with melanoma (CDK4, BAP1, POT1), although pathogenic variants in TP53, CHEK2, and BRCA2 were present in three separate patients and some patients had variants of uncertain significance. In summary, targeted germline sequencing of patients with ≥3 primary melanomas revealed a high rate of pathogenic variants in CDKN2A and other known cancer genes. Although further investigation of these pathogenic variants and variants of uncertain significance is needed, these results support cancer gene panel testing in individuals diagnosed with ≥3 melanomas.

The interplay of sun damage and genetic risk in Australian multiple and single primary melanoma cases and controls

BACKGROUND

Skin phenotype, host genotype and ultraviolet (UV) damage play a role in the development of melanoma.

OBJECTIVES

To ascertain whether the level of UV damage at the site of melanomas was associated with genetic polymorphisms.

METHODS

Deep phenotyping was performed on 1244 individuals; 281 with multiple primary melanomas (MPMs), 304 with single primary melanoma (SPM) and 659 convenience controls. Genotype data was generated using the Illumina CoreExome microarray platform, assaying over 500 000 single-nucleotide polymorphisms. A subset of variants were combined to assess a polygenic risk score (PRS) for melanoma.

RESULTS

Most MPM cases were diagnosed in patients aged > 40 years, in sites with visible chronic UV damage. Women and those diagnosed at age ≤ 40 years were less likely to have perilesional UV damage. Patients with MPM had higher frequencies of MITF E318K, MC1R R-alleles and the ASIP risk haplotype. Individuals who had melanoma in a visibly UV-damaged site were more likely to carry MC1R rs75570604 [odds ratio (OR) 2·5], 9q31.2 rs10816595 (OR 1·4) and MTAP rs869329 (OR 1·4). These same alleles were more common in patients with MPM who were diagnosed at age ≤ 40 years. The mean PRS was significantly higher in MPM than in SPM and controls. Naevus count was comparable in early-onset MPM cases and those diagnosed at age > 40 years.

CONCLUSIONS

Our cohort demonstrated higher frequencies of previously reported alleles associated with melanoma. MPM melanomas more commonly occur in UV-damaged areas, and these individuals are more likely to carry MC1R red hair colour alleles. Awareness of the interplay of genetic vulnerability with UV damage can stratify risk and guide recommendations for melanoma screening. What's already known about this topic? Skin phenotype, host genotype and ultraviolet (UV) damage all play a role in melanoma development. One of the main risk factors is a personal history of melanoma; second and subsequent primary melanomas account for over 20% of all melanomas registered in Queensland. Multiple loci are associated with melanoma risk, including many low-penetrance loci, which may have a cumulatively significant risk. Population-wide screening programmes for melanoma are not yet economically viable. What does this study add? Patients diagnosed with melanoma at age ≤ 40 years were more likely than older patients to have melanomas in non-UV-damaged sites. Patients with multiple melanomas had higher frequencies of MITF E318K, MC1R R-alleles, and the ASIP extended risk haplotype than patients with single melanoma. CDKN2A, MC1R and MTAP variants were more frequent in patients who developed melanomas at a younger age, but also in those whose melanomas were all on visibly UV-damaged sites. What is the translational message? Incorporating these genetic findings into the known risk factors of skin phenotype and visible UV damage may allow for a more customized and economically feasible approach to early detection of melanoma, particularly in younger patients. Plain language summary available online.