RAD51D is a RAD51 paralog that functions as a core component of the BCDX2 complex (RAD51B-RAD51C-RAD51D-XRCC2), playing a critical role in homologous recombination repair (HRR) of double-stranded DNA breaks 1. The BCDX2 complex stimulates nucleation and extension of RAD51 filaments on single-stranded DNA through coupled ATPase activities, orchestrating RAD51 assembly essential for replication fork protection and double-strand break repair 2. RAD51D demonstrates DNA-dependent ATPase activity and binds single-stranded DNA, acting downstream of BRCA2 recruitment and upstream of RAD51 recruitment in the BRCA1-BRCA2-dependent HR pathway. The protein also participates in telomere maintenance via recombination and Holliday junction resolution. Germline pathogenic variants in RAD51D confer significant hereditary cancer risk: cumulative breast cancer risk to age 80 is approximately 20% and tubo-ovarian carcinoma risk is approximately 13% for carriers 3. RAD51D variants associate particularly with estrogen receptor-negative breast cancer and triple-negative breast cancer 45, and contribute to pancreatic cancer susceptibility in Asian populations 6. Among HR genes, RAD51D ranks among the most important ovarian cancer risk genes after BRCA1/BRCA2 7, with biallelic inactivation observed in endometrial cancers harboring germline RAD51D variants 8.