Through our analysis, we demonstrate the non-negligible impact of non-BRCA1/2 mutations in Japanese patients with HBOC syndrome, with the following rates of germline mutations: 8.5% BRCA1, 10.1% BRCA2, 0.2% BRCA1/2, and 6.5% for non-BRCA1/2 genes (5 cases had recurrent variants among 37 patients with non-BRCA1/2 mutations). This evidence concerns the gene BRCA1 and Hereditary breast and ovarian cancer syndrome.