BRCA1 is a multifunctional E3 ubiquitin-protein ligase that mediates Lys-6-linked polyubiquitin chain formation and coordinates diverse cellular pathways essential for genomic stability 1. The BRCA1-BARD1 heterodimer orchestrates DNA damage repair, ubiquitination, and transcriptional regulation by regulating cell cycle checkpoints in S and G2 phases following ionizing irradiation and facilitating homologous recombination repair through interaction with PALB2 and BRCA2-RAD51 machinery 1. BRCA1 also regulates centrosomal microtubule nucleation and inhibits lipid synthesis by preventing ACACA dephosphorylation. Pathogenic BRCA1 variants are responsible for 5-10% of breast cancers and account for the majority of hereditary breast and ovarian cancers 2. Women carrying germline BRCA1 mutations face substantially elevated lifetime breast cancer risk, with MRI surveillance demonstrating significant mortality reduction (hazard ratio 0.20, 95% CI 0.10-0.43) compared to no surveillance 3. Hormonal contraceptive use in BRCA1 carriers increases breast cancer risk with longer cumulative duration (3% increase per additional year) 4, while risk-reducing mastectomy substantially reduces incident cancers with low breast cancer mortality probability (0.95% within 15 years) 5. BRCA1 deficiency impairs DNA end resection through DYNLL1-mediated MRE11 inhibition, reducing homologous recombination capacity 6.