Genomic Landscape of 6597 Hong Kong HBOC Patients: Implications for Beyond-BRCA Multi-Gene Panel Testing and Cancer Surveillance.

Breast cancer remains highly prevalent, where the lifetime risk before age 75 is one in 13. However, known genetic factors were only identified in 14.7% of cases in our Hong Kong Hereditary Breast Cancer Family Registry. Our current local policy for genetic testing does not cover the detection of beyond BRCA1/2. Here we highlight the clinical value of extending testing to beyond BRCA susceptibility genes for improved prevention, diagnosis, and management. We recruited 6597 hereditary breast and ovarian cancer (HBOC) patients from our registry based on family history and clinical criteria. Germline mutations were identified by multi-gene sequencing analysis using next-generation sequencing (NGS). Clinical-pathological characteristics of BRCA and beyond BRCA carriers were compared and the real-world management and surveillance services adopted in Hong Kong were highlighted. In this multi-gene hereditary cancer cohort, germline mutations were identified in 10.9% of cases for BRCA1/2 and 3.5% for beyond BRCA susceptibility genes. These beyond BRCA mutations constitute a considerable proportion of actionable hereditary risk. Notably, PALB2 emerged as the most prevalent non-BRCA gene, followed by TP53, ATM, and BARD1. New cancers or recurrences were detected during their surveillance; the overall pick up rates were 8.3% (PALB2), 29.4% (TP53), 33.3% (PTEN) and 5.6% (BARD1). This study provides the first comprehensive characterization of the beyond BRCA germline landscape in a Hong Kong hereditary cancer cohort and highlights the current need for implementing multi-gene sequencing analysis and surveillance services for HBOC patients, establishing the predominant non-BRCA drivers and providing a robust empirical basis for expanding public genetic screening frameworks.