HRD testing influence eligibility for PARP inhibitors?

• A. HRD testing has no effect on eligibility.
• B. They exclude BRCA-mutant tumors.
• C. HRD testing or germline BRCA mutations support use; some approvals require BRCA mutation, others include broader HRD-positive tumors.
• D. Only germline BRCA testing matters

Answer: (C)

PARP inhibitors exploit the vulnerability created when homologous recombination repair is defective. If BRCA1/2 function is lost, whether due to a germline mutation or a somatic tumor alteration, cells rely more on PARP-mediated repair, so blocking PARP leads to accumulation of DNA damage and tumor cell death. HRD testing looks for this repair deficiency in the tumor, including cases without a BRCA mutation, identifying tumors that may still respond to PARP inhibitors. Clinically, drug approvals reflect this biology: some require a BRCA mutation to qualify, while others extend eligibility to tumors that are HRD-positive regardless of BRCA status. Therefore, HRD testing or germline BRCA mutations can support use, but the exact eligibility depends on the specific approval.