Abstract CT051: Carboplatin and talazoparib combination therapy results in differential efficacy and hematologic toxicity in BRCA-mutated patients
Authors: Dhawan Mallika S. , Aggarwal Rahul , Bartelink Imke , Leng Jim , Thomas Scott , Pawlowska Nela , Stevenson Laurie , Chien Amy Jo , Kelley Robin Kate , Munster Pamela N. 
Published: July 2016

Background: Talazoparib is a novel PARP inhibitor (PARPi) in clinical development. Synergistic anti-tumor effects of PARPi and chemotherapy have been observed in preclinical models. This Phase 1 trial evaluates the tolerability, dose limiting toxicities (DLT) and efficacy of talazoparib in combination with carboplatin in patients with or without germ line DNA repair mutations. We hypothesize that talazoparib may overcome carboplatin resistance but induce greater toxicity in patients with DNA repair defects.

Methods: Talazoparib and carboplatin pharmacokinetics (PK), safety and anti-tumor activity were evaluated in a 3+3 dose escalation design. Genetic testing, PK, pharmacodynamic effects (PD), biomarkers, and alternate dose modeling were evaluated to better understand the interaction of carboplatin and talazoparib.

Results: 24 patients (median age 59y) were enrolled in 4 cohorts and treated with talazoparib 0.75 or 0.1 mg/day and carboplatin AUC 1 or 1.5 for 3/3 or 2/3 weeks. Tumor types included: breast (n = 11), prostate (n = 5), cholangiocarcinoma (n = 2), ovarian (n = 2), bladder (n = 1), adenoid cystic carcinoma (n = 1) and adenocarcinoma of unknown origin (n = 2). Germline mutations were noted in BRCA1 (n = 3), BRCA2 (n = 3), BRIP1 (n = 1), and MSH6 (n = 1) and germ line variants of uncertain significance in BRIP1 (n = 1) and BRCA2 (n = 1). Somatic mutations were found in BRCA2 (n = 1), BAP1 (n = 2) and PALB2 (n = 1). DLTs included fatigue and thrombocytopenia; other non-DLT grade 3/4 toxicities included fatigue (13%), neutropenia (33%), thrombocytopenia (33%), and anemia (58%). Post cycle 1 hematological toxicities required dose delays and reductions in almost all patients. One complete response occurred in a patient with germline BRCA1 (gBRCA1) breast cancer and a partial response (PR) in a gBRCA2 bladder cancer patient; 11 patients (pts) had stable disease (SD) for ?3 months. 5 pts had progressive disease (PD) and 6 pts are not yet evaluable. Of those with PD, 83% had prior platinum therapy, whereas in those with SD or disease response, 46% had prior platinum therapy. Effects of talazoparib/carboplatin on platelet (-11.4% vs. -1.1% P&lt;0.001) and neutrophil counts (-9.1% vs. -3.8% P&lt;0.001) were significantly more profound in gBRCA carriers. Simulations using this model suggest that q4-weekly carboplatin dosing in patients with gBRCA or DNA repair defects and every other week dosing in non-carriers would be more tolerable for the combination.

Conclusions: Mutation carriers in BRCA or other DNA repair genes responded better to this combination than non-carriers. Progression with prior platinum or PARPi did not exclude response or clinical benefit. Talazoparib and carboplatin showed significant hematologic toxicity in those with gBRCA or other germ line DNA repair mutations. Lower dosing frequencies of carboplatin when given with PARPi may be required in gBRCA mutation carriers.

Citation Format: Mallika S. Dhawan, Rahul Aggarwal, Imke Bartelink, Jim Leng, Scott Thomas, Nela Pawlowska, Laurie Stevenson, Amy Jo Chien, Robin Kate Kelley, Pamela N. Munster. Carboplatin and talazoparib combination therapy results in differential efficacy and hematologic toxicity in BRCA-mutated patients. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT051.