Efficacy and safety of abiraterone acetate in an elderly patient subgroup (aged 75 and older) with metastatic castration-resistant prostate cancer after docetaxel-based chemotherapy

Background Metastatic castration-resistant prostate cancer (mCRPC) is a disease that primarily affects older men. Abiraterone acetate (AA), a selective androgen biosynthesis inhibitor, in combination with low-dose prednisone (P) improved overall survival (OS) in a randomised trial in mCRPC progressing after docetaxel versus placebo (PL) plus P. Objective To examine the efficacy and safety of AA plus P versus PL plus P in subgroups of elderly (aged ≥75 yr) (n = 331) and younger patients (<75 yr) (n = 863). Design, setting, and participants We conducted a post hoc analysis of a randomised double-blind PL-controlled study in mCRPC patients progressing after docetaxel chemotherapy. Intervention Patients were randomised 2:1 to AA (1000 mg) plus low-dose P (5 mg twice daily) (n = 797) or PL plus P (n = 398). Outcome measurements and statistical analysis Primary end point was OS. Secondary end points were time to prostate-specific antigen (PSA) progression (TTPP), radiographic progression-free survival (rPFS), and PSA response rate. Treatment differences were compared using the stratified log-rank test. The Cox proportional hazards model was used to estimate the hazard ratio (HR) and 95% confidence interval (CI). The key limitation was the post hoc analysis. Results and limitations Elderly patients treated with AA plus P showed improved OS (HR: 0.64; 95% CI, 0.478-0.853; p = 0.0022), TTPP (HR: 0.76; 95% CI, 0.503-1.155; p = 0.1995), and rPFS (HR: 0.66; 95% CI, 0.506-0.859; p = 0.0019), and higher PSA response rate with relative risk (HR: 4.15; 95% CI, 2.2-8.0]; p ≤ 0.0001) compared with patients treated with PL plus P. Grade 3/4 adverse events occurred in 62% of elderly patients and in 60% of patients aged <75 yr treated with AA plus P. Incidences of hypertension and hypokalaemia, although increased in the AA plus P arm, were similar in both age subgroups and readily managed. Conclusions AA improves OS and is well tolerated in both elderly patients and younger patients with mCRPC following docetaxel, hence providing an important treatment option for elderly patients who may not tolerate alternative therapies with greater toxicity. Trial registration ClinicalTrials.gov, identifier NCT00638690.