A retrospective analysis of clinical factors influencing response to treatment with cabazitaxel in patients with metastatic castration resistant prostate cancer.
281 Background: The TROPIC trial demonstrated that cabazitaxel improves overall survival (OS) in mCRPC patients progressing on or after docetaxel; a setting where both abiraterone and enzalutamide are also approved. We evaluated baseline factors that may help predict prostate specific antigen (PSA) response or PSA progression defined as per the Prostate Cancer Clinical Trials Working Group 2 (PCWG2) criteria and OS in mCRPC patients treated with cabazitaxel. Methods: Forty patients from five centres participated in an early access program and were retrospectively reviewed to capture baseline characteristics, disease history, prior and subsequent treatments, PSA response, and OS. The influence of selected variables on PSA response and OS were evaluated by univariate and multivariate stepwise regression analysis. Results: At cabazitaxel initiation, median age was 65, ECOG 0-1 (90%), median PSA was 216 ng/mL, 25% had visceral disease and 70% had pain. Median number of prior docetaxel cycles was 9 and median time from treatment was 9.6 months (5-14.2). Median number of cabazitaxel cycles was 7 (1-27). Fourteen patients received abiraterone before cabazitaxel. In patients with prior abiraterone treatment there was no impact on PSA response compared to patients with no prior abiraterone. In the multivariate regression analysis, presence of visceral disease, low albumin (≤40g/L), low hemoglobin (<100 g/L) and longer time between last docetaxel dose and start of cabazitaxel were correlated with PSA response to cabazitaxel (p<0.10). Age < 65, BMI ≥ 30kg/m2 and presence of pain were linked to an increased likelihood of PSA progression. None of the factors selected were significantly associated with OS. Conclusions: In routine clinical practice, this study suggests that mCRPC patients with visceral disease and a longer time elapsed between last docetaxel dose and start of cabazitaxel may experience a greater PSA response with cabazitaxel.