Prognostic role of docetaxel-induced reduction of free testosterone serum levels in metastatic prostate cancer patients.

Abstract

144 Background: We have recently demonstrated that a salvage therapy with carboplatin plus weekly docetaxel is effective in docetaxel-refractory prostate cancer (PC) and interferes with testosterone biosynthesis (Reuter et al.; Oncol Res & Treat. 2018, 41 (suppl.1): p.10). In this study, the impact of docetaxel monotherapy on free and total testosterone serum levels (fT, TT) and the prognostic role of fT and TT were analyzed in mPC patients. Methods: 62 consecutive mPC patients were treated with at least two cycles of docetaxel (75 mg/m2 q3w; 50 mg/m2 q2w, or 35 mg/m2 q1w) until disease progression, occurrence of intolerable adverse effects or completion of the planned cycle number. Efficacy measures were done following PCWG2 recommendations. FT and TT were measured before and during chemotherapy. Results: At the current analysis (August 31, 2020), the median follow-up time was 21.2 months. Response of prostate-specific antigen (PSAR; ≥50% PSA reduction) was observed in 42/62 (67.7%) and 12/36 (33.3%) patients with measurable disease exhibited a partial remission (PR). Median progression-free survival (PFS) for all patients was 8.1 months (CI 95% 3.6, 12.5) and median overall survival (OS) was 25.7 months (CI 95% 19.4, 32.1). The most common reversible grade 3/4 toxicity was leukopenia/neutropenia (29/33.9%). Median fT and TT serum levels were reduced below the detection limit during docetaxel treatment (fT: from 0.34 pg/mL to < 0.01 pg/mL and TT: from 0.12 to < 0.05 ng/mL, respectively). Multivariate Cox regression analyses identified PSAR > 50%, fT reduction of 100% and number of organs involved as independent prognostic risk factors for PFS. Furthermore, fT reduction of 100% and FT nadir values < 0.01 pg/mL were independent prognostic risk factors for OS (p < 0.05). Conclusions: These data demonstrate that fT is an important prognostic factor for PFS and OS in mPC patients.