Four cancer cases with pathological germline variant <i>RAD51D</i> c.270_271dup

Pathological germline variants (PGVs) of RAD51D increase the risk of breast and ovarian cancer. In East Asia, c.270_271dup is the most frequently detected PGV of RAD51D; however, only a few cases have been reported in Japan. We report four cancer cases with a germline RAD51D c.270_271dup PGV. Three of them (lung cancer: 2, oral cancer: 1) were incidentally identified by whole genome sequencing in patients negative for the associated cancer histories, homologous recombination (HR) deficiency, or a second hit of RAD51D in the cancer DNA. For genetic counseling, we provided information on surveillance and cascade testing based on Western guidelines. The PGVs of moderate-risk HR-related genes are difficult to detect based on phenotype, especially in male-predominant pedigrees. The current spread of cancer genomic analysis will increase opportunities for incidental variant identification. The establishment of Japanese guidelines is expected to aid in the management of PGV carriers of moderate-risk genes.