Inherited breast cancer predisposition in Asians: multigene panel testing outcomes from Singapore.

Genetic testing for germline mutations in breast cancer predisposition genes can potentially identify individuals at a high risk of developing breast and/or ovarian cancer. There is a paucity of such mutational information for Asians. Panel testing of 25 cancer susceptibility genes and deletion/duplication analysis was performed for 220 Asian breast cancer patients or their family members referred for genetics risk assessment. All 220 participants had at least one high-risk feature: having a family history of breast and/or ovarian cancer in first- and/or second-degree relatives; having breast and ovarian cancer in the same individual or bilateral breast cancer; having early-onset breast cancer or ovarian cancer (⩽40 years of age). We identified 67 pathogenic variants in 66 (30.0%) patients. Of these, 19 (28.3%) occurred in , 16 (23.9%) in , 7 (10.4%) in , 6 (9.0%) in , 2 (3.0%) in , 2 (3.0%) in and 15 (22.4%) in other predisposition genes. Notably, 47.8% of pathogenic variants were in non- genes. Of the 66 patients with pathogenic mutations, 63.6% (42/66) were under the age of 40 years. Family history of breast and/or ovarian cancer is enriched in patients with pathogenic variants but less predictive for non- related pathogenic variations. We detected a median of three variants of unknown significance (VUS) per gene (range 0-21). Custom gene panel testing is feasible and useful for the detection of pathogenic mutations and should be done in the setting of a formal clinical cancer genetics service given the rate of VUS.