Background: BRCA-mutated tumors are more susceptible to platinum therapy and PARP inhibitors due to underlying defects in homologous recombination repair of DNA damage. In preclinical models the potent oral PARP1/2 inhibitor veliparib was shown to enhance sensitivity to C and to have single-agent activity in BRCA+ cell lines. Phase 1 trials suggest promising antitumor activity and acceptable toxicity of veliparib plus C/P in triple-negative BC (Puhalla et al. Cancer Res 2012;72[24 suppl]:PD09-06) and single-agent activity of veliparib in BRCA+ BC (Somlo et al. J Clin Oncol 2014;32[15 suppl]:abstr. 1021). This phase 3 trial assesses efficacy and toxicity of veliparib plus C/P vs C/P alone in patients with HER2−BRCA-associated locally advanced or metastatic BC (NCT02163694). Methods: Phase 3 randomized, double-blind, placebo-controlled, multicenter trial. Eligible patients (female or male; ≥ 18 years) have HER2−metastatic/locally advanced unresectable BC with (suspected) deleterious BRCA1/2 germline mutations and received 2 or fewer prior lines of DNA-damaging chemotherapy for metastatic BC. In addition, patients must have received ≤ 1 prior line of platinum therapy (any setting) without progression within 12 months of completing treatment. Patients are randomized 2:1 to C/P with veliparib or C/P with placebo, stratified by estrogen and/or progesterone receptor expression, prior platinum therapy, and central nervous system metastases. Veliparib (120 mg p.o. BID) or placebo will be given on Days −2 to 5, C (AUC 6 mg/mL/min i.v.) on Day 1, and P (80 mg/m² i.v.) on Days 1, 8, and 15 (21-day cycles). Treatment continues until unacceptable toxicity or progressive disease (PD). Patients in the placebo arm who discontinue due to PD are eligible for crossover to veliparib monotherapy. The primary objective is to assess if the addition of veliparib to C/P increases progression-free survival; additional objectives include evaluation of overall survival, clinical benefit rate, objective response rate, quality of life, and safety. Enrollment began in July 2014 with a planned sample size of 270 patients. Clinical trial information: NCT02163694