BRCAness and Merkel cell carcinoma: Comprehensive molecular study of 35 cases and meta-analysis of the literature

Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous neuroendocrine cancer. Management of advanced MCC is mainly based on immune-checkpoint inhibitors (ICI). The high failure rate (up to 75%) warrants investigation of new therapeutic targets. The recent identification of BRCA1 or BRCA2 (BRCA1/2) mutations in some MCC raises the issue of the use of poly-(ADP-Ribose)-polymerase inhibitors (PARPi) in selected advanced cases. The main objective of our study is to determine the accurate frequency of BRCA1/2 pathogenic variants. We studied a novel series of 35 MCC and performed a meta-analysis of BRCA1/2 variants of published cases in the literature. In our series, we detected only one BRCA2 pathogenic variant (nonsense mutation; ENIGMA class 5) and one BRCA2 variant of unknown significance (VUS). The low frequency of BRCA1/2 pathogenic variants in our series of MCC (3%) was confirmed by the meta-analysis of BRCA1/2 variants of the literature. Among the 204 MCC studied for molecular alterations of BRCA1/2, only two BRCA1 pathogenic nonsense mutations were identified (1%), while the vast majority of BRCA1/2 variants were missense mutations classified as VUS. BRCA1/2 pathogenic variants are uncommon in MCC. However, in BRCA-mutated-MCC, PARPi might be a valuable therapeutic option requiring validation by clinical trials. Merkel cell carcinoma