BRCA2 DNA repair associated

BRCA2 DNA repair associated (BRCA2) is a tumor suppressor gene on chromosome 13q12.3 encoding a large nuclear protein of approximately 3,418 amino acid residues. Its central role is in homologous recombination repair (HRR), the high-fidelity mechanism that mends double-strand breaks using an undamaged sister chromatid as template. BRCA2 is the loader in that reaction: through its BRC repeats and C-terminal domain it binds RAD51 recombinase, delivers it to resected single-stranded DNA in place of replication protein A, and stabilizes the nucleoprotein filament that performs strand invasion. A second, separable function protects stalled replication forks from nucleolytic degradation, so cells lacking BRCA2 lose both the ability to repair breaks accurately and the ability to preserve forks under replication stress. Biallelic inactivation, through germline and somatic loss-of-function pathogenic variants (PVs), leaves the cell dependent on error-prone repair, producing the chromosomal aberrations, genomic instability, and loss of heterozygosity that mark hereditary and sporadic cancers. Inherited biallelic BRCA2 mutation is instead compatible with development and causes Fanconi anemia complementation group D1.

Alongside its close functional partner BRCA1, BRCA2 is among the most clinically significant cancer predisposition genes known; germline carriers face substantially elevated lifetime risks of breast cancer, ovarian cancer, pancreatic and prostate cancer, among others. One inherited variant is not itself sufficient — the wild-type allele is typically lost in the tumor — which is why HRR deficiency is a property of the cancer cell rather than of every cell in the carrier.

That deficiency is also the therapeutic opening. HRR-deficient cells cannot resolve the double-strand breaks that arise when replication forks meet unrepaired single-strand damage, which makes them selectively sensitive to crosslinking agents such as cisplatin and carboplatin, and synthetically lethal with inhibition of Poly(ADP-ribose) polymerase 1 (PARP1). The lethality is driven less by loss of PARP's catalytic role in single-strand break repair than by trapping: a PARP inhibitor such as olaparib or niraparib locks PARP1 onto damaged DNA, and the trapped complex collapses the oncoming replication fork into a break the cell cannot repair. Resistance commonly arises through secondary reversion mutations that restore the BRCA2 reading frame, and the same logic has been extended beyond mutation carriers to tumors with HRR deficiency from other causes.