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Background Sipuleucel-T is an autologous cell-based cancer immunotherapy for men with asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). Its approval by the Food and Drug Administration was based on demonstration of an overall survival (OS) benefit in randomized placebo-controlled phase III trials. However, treatment was associated with a prostate-specific antigen (PSA) decline in only a small minority of patients. Understanding the clinical factors that are associated with OS could help guide treatment decisions, including patient selection and the timing of sipuleucel-T relative to other therapies. Patients and Methods We retrospectively identified 94 mCRPC patients treated with sipuleucel-T from April 2010 to April 2016. The Kaplan-Meier method was used to estimate the distribution of OS. Univariate and multivariate Cox proportional hazard modeling was used to identify the prognostic factors for OS. Results With a median follow-up of 24.9 months, the median OS was 34.9 months. On multivariate analysis, Eastern Cooperative Oncology Group performance status, pretreatment PSA doubling time, and previous abiraterone and/or enzalutamide were significant prognostic factors for OS. Conclusion A poorer baseline performance status, faster disease pace measured by the PSA doubling time, and previous novel androgen signaling inhibitor exposure could be important prognostic considerations for the treatment of mCRPC patients with sipuleucel-T. Further studies are needed to validate these findings.

Background Abiraterone acetate (AA) inhibits androgen biosynthesis and prolongs survival in men with metastatic castration-resistant prostate cancer (mCRPC) when combined with prednisone (P). Resistance to therapy remains incompletely understood. In this open-label, single-arm, multicenter phase II study we investigated the clinical benefit of increasing the dose of AA at the time of resistance to standard-dose therapy. Patients and Methods Eligible patients had progressive mCRPC and started AA 1000 mg daily and P 5 mg twice daily. Patients who achieved any prostate-specific antigen (PSA) decline after 12 weeks of therapy continued AA with P until PSA or radiographic progression. At progression, AA was increased to 1000 mg twice daily with unchanged P dosing. Patients were monitored for response to therapy for a minimum of 12 weeks or until PSA or radiographic progression. The primary end point was PSA decline of at least 30% after 12 weeks of therapy at the increased dose of AA. Results Forty-one patients were enrolled from March 2013 through March 2014. Thirteen men experienced disease progression during standard-dose therapy and were subsequently treated with AA 1000 mg twice per day. Therapy was well tolerated. No PSA declines ≥ 30% nor radiographic responses were observed after 12 weeks of dose-escalated therapy. Higher baseline dehydroepiandrosterone levels, lower circulating tumor cell burden, and higher pharmacokinetic levels of abiraterone and abiraterone metabolites were associated with response to standard-dose therapy. Conclusion Increasing the dose of abiraterone at the time of resistance has limited clinical utility and cannot be recommended. Lower baseline circulating androgen levels and interpatient pharmacokinetic variance appear to be associated with primary resistance to AA with P.