Prevalence and reclassification of BRCA1 and BRCA2 variants in a large, unselected Chinese Han breast cancer cohort.

Accurate interpretation of BRCA1/2 variants is critical for risk assessment and precise treatment of breast cancer (BC). Hence, the establishment of an ethnicity-based BRCA1/2 variant database of the Chinese population is of paramount importance. In this study, panel-based sequencing served to detect BRCA1/2 variants in a Chinese multicenter cohort of 21,216 BC patients and 6434 healthy controls. Overall, the percentage of subjects carrying pathogenic variants was 5.5% (1174/21,216) in BC patients and 1.1% (71/6434) in healthy controls. We identified 13 pathogenic variants as high-frequency variants that had a frequency of > 0.45‰ in BC patients (≥ 10 in 21,216 patients), none of which has been reported in Caucasians. Pathogenic BRCA1/2 variants correlated with younger onset age, higher frequencies of bilateral and triple-negative BC (TNBC), invasive carcinomas, high histological grades, and family history of BC and other cancers. Furthermore, the percentage of the subjects carrying VUS was 9.8% (2071/21,216) in BC patients and 6.9% (446/6434) in healthy controls. Based on our cohort study, we unambiguously reclassified 7 out of the 858 VUS resulting in lower VUS ratio in patients (from 9.8 to 7.9%) as well as in healthy control (from 6.9 to 5.3%). We also re-analyzed the 100 variants in 13 exons (2-5 and 15-23) of the BRCA1 genes using a functional assay (saturation genome editing; SGE). 55 of the 59 VUS had distinct status in the SGE study: 24 (43.6%) were pathogenic, and 31 (56.4%) were benign. Strong ethnicity-specific occurrences of pathogenic BRCA1/2 variants were identified in the Chinese population. Hence, the findings provide rationale and sequencing information for the implementation of BRCA1/2 variants tailored to the Chinese population into clinical risk assessment.