Prolonged PSA stabilization and overall survival following sipuleucel-T monotherapy in metastatic castration-resistant prostate cancer patients

BACKGROUND: Sipuleucel-T is an autologous cellular immunotherapy that is FDA approved for the treatment of asymptomatic or minimally symptomatic metastatic castrate-resistant prostate cancer (mCRPC). The IMPACT registry trial demonstrated a 4.1 month survival benefit, but not a consistent PSA response or improvement in progression-free survival. Based upon several factors, including this lack of objective treatment response, sipuleucel-T has been under-utilized in this patient population, despite current NCCN recommendations. METHODS: In order to explore if delayed treatment response occurs in a subset of patients, we performed a single institutional retrospective analysis of mCRPC patients treated with sipuleucel-T and ongoing ADT alone. Within that group, we then identified a subset of sipuleucel-T-treated men with long-term disease control and no additional interventions. To independently confirm this finding, we evaluated a total of 336 patients from 4 large urology group practices treated with sipuleucel-T between 2010 and 2014 and identified 44 patients who met the same criteria and demonstrated evidence of PSA stabilization post sipuleucel-T treatment. RESULTS: For this subgroup of patients, 79% (95% CI: 64.5%, 88.1%) survived 36 months with a median time to subsequent therapy of 17.8 months (95% CI 10.3, 25.3). CONCLUSIONS: Although patient selection could account for some or all of these results, these data support the utilization of sipuleucel-T alone in select mCRPC patients that is associated with a delay in disease progression and a good overall prognosis.