PurposeTo understand the broader genetic landscape of Male Breast Cancer (MBC), focusing on the utility of genome sequencing (GS) beyond BRCA1/2 (HGNC: 1100, 1101) variants. Methods24 MBC patients underwent a multi-step genetic analysis. Initial screening targeted BRCA1/2 variants followed by GS to identify pathogenic/likely pathogenic (P/LP) germline variants through a three-tiered classification. Polygenic risk score (PRS) analysis was further incorporated using a model for female breast cancer with 2666 non-cancer controls. Exome sequencing (ES) was employed to transition from germline to somatic investigations, assessing second-hit variant and mutational signatures. ResultsThe GS analysis unveiled previously unrecognized P/LP germline variants in BARD1, ATR, BRIP1, and CHEK2 (HGNC: 952, 882, 20473, 16627) among 21 BRCA1/2-negative MBC patients, elevating the diagnostic yield from 12.5% to 33.0% in all MBC. Elevated average PRS was noted compared to controls, with a significant correlation to early-onset MBC when combined with high-penetrance germline pathogenic variants (P = 1.10×10-4). ES analysis further identified significant somatic oncogenic drivers and revealed a dominant mutational signature SBS3 across BRCA1/2-negative samples, reinforcing the contribution of HRD underlying the MBC development. ConclusionOur findings extended the MBC genetic spectrum beyond BRCA1/2 and highlighted the intricate interplay of monogenic and polygenic predispositions, presenting a comprehensive MBC genomic profile.
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