Abstract
341 Background: Sipuleucel-T is an autologous cellular immunotherapy approved for patients with symptomatic or minimally asymptomatic metastatic castration-resistant prostate cancer based on prolongation of overall survival. We sought to retrospectively analyze the type and time to next-line therapy after the initiation of Sipuleucel-T (Sip-T) in the era of multiple new other therapeutic compounds that became available since approval of Sip-T to better understand the context of utilization of this immunotherapy in the current era. Methods: We performed a retrospective analysis of 53 patients with metastatic prostate cancer (PC) who have been treated with Sip-T at The City of Hope Medical Center between September 2010 and April 2013 and subsequently received another therapy. Variables included age at Sip-T treatment, Karnofsky Performance Score (KPS), Gleason score at diagnosis, extent of metastatic disease (limited or extensive), and white blood cell (WBC) count pre and post (Sip-T). PSA was measured at six time points (3 pre and 3 post Sip-T) and these were analyzed using a mixed linear regression model. A Cox Proportional Hazard model was used to examine predictors of time in days to next therapy as a function of the above variables including mixed model slopes of PSA. Results: Kaplan – Meier estimated median time to next treatment among the 53 patients was 122 days (95% CI, 86-177 days) and was significantly predicted by slope of PSA from the mixed model (HR = 25.883, p < .0001), WBC post therapy (HR = 1.352, p = 0.0017), and age at Sip-T (HR = 1.044 p = 0.0492). KPS, Gleason score, pre Sip-T WBC, and the extent of metastatic disease were not predictive. Most patients had abiraterone acetate for next treatment (n = 32, 58.2%). Other treatments included docetaxel (n = 5, 9.1%), orteronel with prednisone or prednisone alone (n = 12, 21.8%), and others (n = 6, 10.9%). Conclusions: In our experience median time to subsequent therapies was shorter than reported in pivotal Phase III study. Shorter time to post-Sip-T therapy was associated with older age, higher levels of WBC post-Sip-T therapy and more rapid rate of increase in the PSA level.
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