Results from a Phase 2 Study of Induction Docetaxel and Carboplatin Followed by Maintenance Rucaparib in the Treatment of Patients with Metastatic Castration-resistant Prostate Cancer with DNA Homologous Recombination Repair Deficiency.

Background and objective: Our aim was to determine whether induction chemotherapy followed by PARP inhibitor (PARPi) maintenance improves outcomes for patients with metastatic castration-resistant prostate cancer (mCRPC) harboring alterations in homologous recombination repair (HRR) genes in comparison to a historical control cohort treated with PARPi monotherapy.

Methods: This single-arm, open-label, investigator-initiated phase 2 trial (NCT02985021) enrolled 18 patients with mCRPC with pathogenic alterations in HRR genes between 2018 and 2021 at a single center. Patients received four cycles of induction chemotherapy with docetaxel (60 mg/m²) and carboplatin (area under the curve 5) every 21 d, followed by maintenance rucaparib (600 mg twice daily) until progression or unacceptable toxicity. The primary outcome was radiographic progression-free survival (rPFS). Subsequent to study inception, multiple other studies reported alterations in genes of the BRCA complex (BRCA-C: BRCA1, BRCA2, PALB2) as most predictive of PARPi response; therefore, a post hoc analysis comparing patients with alterations in BRCA-C genes to a historical control cohort was performed.

Key findings and limitations: After median follow-up of 40.3 mo (interquartile range 38.5-not reached [NR]), the median rPFS for all patients was 8.1 mo (95% confidence interval [CI] 6.5-31.2), similar to a historical control cohort treated with PARPi monotherapy. Among the 12 patients with BRCA-C alterations, median rPFS was 17.7 mo (95% CI 7.5-NR; p = 0.05). A key limitation is the single-arm design.

Conclusions and clinical implications: Induction platinum-based chemotherapy followed by maintenance PARPi therapy did not improve outcomes for patients with mCRPC broadly selected for HRR deficiency. However, results were promising in the more stringently selected group with BRCA-C gene alterations. Further studies comparing this approach to PARPi monotherapy are warranted.