TALAPRO-1: An open-label, response rate phase II study of talazoparib (TALA) in men with DNA damage repair (DDR) defects and metastatic castration-resistant prostate cancer (mCRPC) who previously received taxane-based chemotherapy (CT) and progressed on greater than or equal to one novel hormonal therapy (NHT).

Abstract

TPS342 Background: There are no approved therapies for mCRPC that has progressed on taxane and NHT. Preclinical studies showed that DDR-positive prostate tumors may be sensitized to PARP inhibition. TALA inhibits PARP, causing cell death in BRCA1/2-mutated cells. Methods: This study (NCT03148795) is enrolling patients (pts) (N ≈ 100) with measurable soft tissue disease per RECIST v1.1, progressive mCRPC, DDR likely to sensitize to PARP inhibition, ECOG performance status ≤ 2, and no brain metastases, who received 1-2 CT regimens (including ≥ 1 taxane-based CT) and progressed on ≥ 1 NHT (enzalutamide/abiraterone acetate). Prior use of PARP inhibitors, cyclophosphamide, mitoxantrone, or platinum-based CT ≤ 6 mos before study or progression on a platinum-based CT at any time are excluded. Pts will receive TALA 1 mg/d orally (pts with moderate renal impairment, 0.75 mg/d) until radiographic progression, unacceptable toxicity, or withdrawal of consent. TALA should not be discontinued based on increased prostate specific antigen (PSA) or circulating tumor cell (CTC) count alone. Primary endpoint is best objective response (OR) rate (complete/partial soft tissue response; exact 2-sided 95% confidence interval). Responses must be confirmed ≥ 4 wks later by computed tomography/magnetic resonance imaging with no evidence of bone progression ≥ 6 wks later per PCWG3 criteria. Secondary endpoints include time to OR, duration of response, PSA decrease ≥ 50%, CTC count conversion (to CTC = 0 and < 5 per 7.5 mL of blood), time to PSA progression, radiographic progression-free survival, overall survival, safety, pt-reported outcomes, and pharmacokinetics of TALA. Efficacy will be assessed every 8 wks for the first 24 wks, then every 12 wks thereafter. An initial safety and efficacy analysis will be performed on 20 pts after ≥ 8 wks of treatment. An interim efficacy analysis is planned when 60 pts have completed ≥ 6 mos of treatment. This study was sponsored by Pfizer Inc. Previously presented at ESMO 2018, FPN 859TiP, De Bono JS et al. Reused with permission. Clinical trial information: NCT03148795.