In this study, two datasets were used to analyze metastatic castration-resistant prostate cancer (mCRPC) patients managed with sipuleucel-T who did not immediately start subsequent therapy. Findings revealed delayed PSA response in a subset of patients suggesting delayed clinical activity.

• Sipuleucel-T has shown survival advantage in phase 3 trials but is employed in few men with mCRPC partially because of low rates of PSA and objective response.

• Among 1902 men who underwent treatment for mCRPC in PROCEED (an FDA-requested outcomes registry) and 255 patients treated consecutively with sipuleucel-T at Dana-Farber Cancer Institute (DFCI), 171 and 28 patients were included, respectively.

• All patients exhibited increasing PSA before initiating sipuleucel-T and available post-treatment PSA measurements.

• Clinical results of interest were: PSA ₅₀ response rate, time to subsequent mCRPC directed therapy, and overall survival (OS).

• In the PROCEED cohort, 19.9% demonstrated PSA ₅₀ response at a median of 5.5 months (IQR: 3.9–9.5) since the last sipuleucel-T infusion; median time to subsequent mCRPC directed therapy and median OS were 10 months (95% CI: 9–11) and 49 months (95% CI: 43–NR), respectively.

• In the DFCI cohort, 14.3% demonstrated PSA ₅₀ response at a median of 6.3 months (IQR: 4.7–7.0); median time to subsequent mCRPC directed therapy and median OS were 9 months (95% CI: 9–11) and 60 months (95% CI: 51–74), respectively.