BRCA1/2 mutations are not a common cause of malignant melanoma in the Polish population

Abstract

The association of BRCA1/2 mutations with melanoma is not completely determined; the interpretation of variants of unknown significance is also problematic. To evaluate these issues we explored the molecular basis of melanoma risk by performing whole-exome sequencing on a cohort of 96 unrelated Polish early-onset melanoma patients and targeted sequencing of BRCA1/2 genes on additional 30 melanoma patients with familial aggregation of breast and other cancers. Sequencing was performed on peripheral blood. We evaluated MutationTaster, Polyphen2, SIFT, PROVEAN algorithms, analyzed segregation with cancer disease (in both families with identified BRCA2 variants) and in one family performed LOH (based on 2 primary tumors). We found neither pathogenic mutations nor variants of unknown significance within BRCA1. We identified two BRCA2 variants of unknown significance: c.9334G>A and c.4534 C>T. Disease allele frequency was evaluated by genotyping of 1230 consecutive melanoma cases, 5000 breast cancer patients, 3500 prostate cancers and 9900 controls. Both variants were found to be absent among unselected cancer patients and healthy controls. The MutationTaster, Polyphen2 and SIFT algorithms indicate that c.9334G>A is a damaging variant. Due to lack of tumour tissue LOH analysis could not be performed for this variant. The variant segregated with the disease. The c.4534 C>T variant did not segregate with disease, there was no LOH of the variant. The c.9334G>A variant, classified as a rare variant of unknown significance, on current evidence may predisposes to cancers of the breast, prostate and melanoma. Functional studies to describe how the DNA change affects the protein function and a large multi-center study to evaluate its penetrance are required.

Fig 1. Pedigree of the family with c.9334G>A detected variant.

* age. Abbreviation: Pr, prostate cancer; Leu, leukemia; Br, breast cancer; Thr, thyroid cancer; CRC, colorectal cancer; Liv, liver cancer; (+), mutation positive; (-), mutation negative; (ne), not examined.

Fig 2. Pedigree of the family with c.4534 C>T detected variant.

* age. Abbreviation: Leu, leukemia; Br, breast cancer; Lu, lung cancer; CRC, colorectal cancer; (+), mutation positive; (-), mutation negative; (ne), not examined.