Functional Analysis of BARD1 Missense Variants on Homology‐Directed Repair in Ovarian and Breast Cancers

ABSTRACT Women with germline BRCA1 mutations face an increased risk of developing breast and ovarian cancers. BARD1 (BRCA1 associated RING domain 1) is an essential heterodimeric partner of BRCA1, and mutations in BARD1 are also associated with these cancers. While BARD1 mutations are recognized for their cancer susceptibility, the exact roles of numerous BARD1 missense mutations remain unclear. In this study, we conducted functional assays to assess the homology‐directed DNA repair (HDR) activity of all BARD1 missense substitutions identified in 55 breast and ovarian cancer samples, using the real‐world data from the COSMIC and cBioPortal databases. Seven BARD1 variants (V85M, P187A, G491R, R565C, P669L, T719R, and Q730L) were confirmed to impair DNA damage repair. Furthermore, cells harboring these BARD1 variants exhibited increased sensitivity to the chemotherapeutic drugs, cisplatin, and olaparib, compared to cells expressing wild‐type BARD1. These findings collectively suggest that these seven missense BARD1 variants are likely pathogenic and may respond well to cisplatin‐olaparib combination therapy. This study not only enhances our understanding of BARD1's role in DNA damage repair but also offers valuable insights into predicting therapy responses in patients with specific BARD1 missense mutations.