Assessing olaparib efficacy in U.S. Veterans with metastatic prostate cancer utilizing a time-indifferent g-rate method ideal for real-world analyses

We aimed to assess real-world efficacy of the PARP inhibitor, olaparib, in US Veterans with metastatic prostate cancer (mPC) by leveraging the national data repository and evaluate a novel approach to assess treatment efficacy in tumors considered rare or harboring rare mutations. Included Veterans had 1) mPC with somatic or germline alterations/mutations in genes involved in homologous recombination repair (HRR), 2) received olaparib monotherapy as well as a novel hormonal therapy/androgen receptor pathway inhibitors (NHT/ARPI), and/or chemotherapy, and 3) estimable rates of tumor growth (g-rate) using PSA values obtained while receiving treatment. Previous work has shown an excellent inverse correlation of g-rate with survival. Using g-rate, we determined tumor doubling time (DT) and DT ratios (DT on olaparib/DT on prior medication). We postulated that a DT ratio≥ 1 was associated with benefit. We identified 139 Veterans, including 42 Black males with tumors harboring mutations/alterations in HRR genes who received olaparib: BRCA2 (50), ATM (32), BRCA1 (10), other mutations (47). 62/139 (45%) of all and 21/42 (50%) of Black Veterans had DT ratios ≥1, including 31, 10, 2, and 19 with BRCA2, ATM, BRCA1, and other mutations, respectively (p = 0.006). Median survival with DT ratios ≥1 was superior, being 24.5 vs. 11.4 months for DT ratio