Clinical variables associated with overall survival in metastatic castration resistant prostate cancer (mCRPC) patients treated with sipuleucel-T immunotherapy.

Abstract

e16565 Background: Sipuleucel-T (Sip-T) is a cellular-based cancer immunotherapy for men with asymptomatic or minimally symptomatic mCRPC. Its approval was based on overall survival (OS) benefit in randomized placebo-controlled phase 3 trials. However, treatment was associated with PSA decline in only a small minority of pts. Understanding clinical factors predictive of OS may help to guide treatment decisions, including pt selection and timing of Sip-T relative to other therapies. Methods: This is a retrospective chart review of mCRPC pts treated with Sip-T at UCSF between April 2010 and April 2016. All pts completed 3 Sip-T infusions. Patients with localized prostate cancer treated with neoadjuvant Sip-T (NCT00715104) and pts with mCRPC treated with an ongoing phase 2 Sip-T/Ipilimumab trial (NCT01804465) were excluded. Kaplan-Meier method was used to estimate OS. The predictive value of candidate variables – including age, ECOG performance status (PS), Gleason score, metastatic volume, baseline PSA, baseline PSADT, prior abiraterone or enzalutamide, and prior chemotherapy – was assessed using univariate and multivariate Cox proportional hazard model. Results: Of 43 patients evaluated to date, 74.4% had ECOG PS 0, 88.4% had bone +/- nodal metastasis, 81.4% had low metastatic volume, 9.3% had prior abiraterone, 2.3% had prior enzalutamide, and 9.3% had prior chemotherapy. The median age was 69 years (range 53-85), median baseline PSA was 8.3 ng/mL (range 0.05-227.9) and median PSA doubling time (PSADT) was 3.9 mo (range 1.4-15.1). At a median follow-up of 21.4 mo, the median OS was 34.1 mo (95% CI 25.7-41.4). Univariate analysis showed that ECOG PS (HR 6.66, p < 0.001) and PSA (log-transformed) (HR 3.36, p = 0.002) were significantly associated with OS. There was a trend towards worse OS with faster baseline PSADT (log-transformed) (HR 0.16, p = 0.11) and prior chemotherapy (HR = 4.13, p = 0.11). By multivariate analysis, ECOG PS, baseline PSA and baseline PSADT were statistically significant (p < 0.05). Conclusions: In this ongoing retrospective cohort, ECOG PS, baseline PSA and baseline PSADT were associated with OS in mCRPC patients treated with Sip-T.