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 BRCA1/2 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 BRCA1, 16 (23.9%) in BRCA2, 7 (10.4%) in PALB2, 6 (9.0%) in TP53, 2 (3.0%) in PTEN, 2 (3.0%) in CDH1 and 15 (22.4%) in other predisposition genes. Notably, 47.8% of pathogenic variants were in non-BRCA1/2 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 BRCA1/2 pathogenic variants but less predictive for non-BRCA1/2 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.