Genomic Insights: How BRCA2 Inherited Variants Drive Drug Resistance

In an interview with Targeted Oncology, Pedram Razavi, MD, PhD, breast medical oncologist and director of Liquid Biopsy & Genomics at Memorial Sloan Kettering Cancer Center, discusses how the paradigm of breast cancer research is shifting by exploring how germline variants dictate the way a tumor evolves and resists treatment. Since 2013, researchers at MSK has sequenced over 10,000 tumors, providing a massive dataset that finally allows scientists to distinguish the biological impacts of BRCA1 vs BRCA2 mutations, a distinction often missed in smaller studies.

The findings are striking: while BRCA1-associated tumors are enriched with TP53 mutations, BRCA2 tumors are significantly more likely to lose the RB1 gene. This is a major problem because RB1 is a primary gatekeeper for the cell cycle; its loss makes the cancer effectively "immune" to CDK4/6 inhibitors. The research reveals an evolutionary shortcut: because BRCA2 and RB1 both reside on chromosome 13q, the process that disables the healthy copy of BRCA2 often inadvertently deletes one copy of RB1 as well. This leaves the tumor just one "hit" away from total resistance, a barrier it easily clears under the selective pressure of therapy.

Clinically, this suggests that the current standard of care—starting with CDK4/6 inhibitors and saving PARP inhibitors for later—might be backward for BRCA2 carriers. Data from animal models and patient-derived xenografts indicate that frontline PARP inhibitors may offer better progression-free survival. This hypothesis is currently being tested in the EvoPAR-Breast01 phase 3 clinical trial.

Looking forward, clinicians look to move from a reactive "wait and see" approach to a proactive interception model. By using AI and ultra-sensitive ctDNA monitoring, clinicians hope to predict a tumor's likely evolutionary path and block its escape routes before resistance even takes hold. As it turns out, the best way to win a game of evolutionary chess is to stop the opponent from making their move in the first place.

REFERENCE

Safonov A, Lee M, Brown DN, et al. Homologous recombination deficiency and hemizygosity drive resistance in breast cancer. Nature. 2026 Apr;652(8110):752-762. doi: 10.1038/s41586-026-10197-0. Epub 2026 Mar 4. PMID: 41781623; PMCID: PMC13083263.