The intersection of genetic risk factors may fundamentally alter how clinicians assess breast cancer susceptibility in men, particularly those developing the disease before age 50. This paradigm becomes critical as male breast cancer, while representing only 1% of cases globally, often presents with more aggressive hormone-driven characteristics than female variants.
A 42-year-old man developed estrogen receptor-positive invasive breast carcinoma despite carrying what would traditionally be considered moderate genetic risk factors. Comprehensive genetic analysis revealed a CHEK2 nonsense variant, a likely pathogenic MSH6 frameshift mutation, and crucially, a polygenic risk score placing him in the 99th percentile for breast cancer susceptibility. Tumor analysis showed microsatellite stability, effectively ruling out the MSH6 variant as a primary driver.
This case demonstrates how polygenic risk scores—computational models aggregating effects from hundreds of common genetic variants—may transform cancer risk assessment when combined with established moderate-penetrance mutations like CHEK2. Traditional genetic counseling focuses primarily on high-penetrance variants in genes like BRCA1 and BRCA2, but this approach may miss substantial risk conferred by the cumulative burden of common variants. The 99th percentile polygenic score likely amplified the moderate risk from the CHEK2 variant, creating a perfect storm for early-onset disease. Current clinical practice rarely incorporates polygenic scoring into routine cancer risk assessment, despite mounting evidence of its predictive value. This oversight may leave many individuals with elevated but unrecognized cancer susceptibility outside standard surveillance protocols, particularly men who face lower baseline screening recommendations than women.