64 Background: Sipuleucel-T is an autologous cellular immunotherapy indicated for asymptomatic or minimally symptomatic mCRPC based on data from the pivotal phase 3 IMPACT trial that demonstrated a 22% reduction in the risk of death. Given the high prevalence of older men in the mCRPC patient (pt) population, we sought to understand disease characteristics and sipuleucel-T product parameters in pts ≥80 years (yrs). Methods: PROCEED is an ongoing phase 4 registry enrolling pts treated with sipuleucel-T within ≤6 months. Baseline pt demographics and disease characteristics were collected. Sipuleucel-T product parameters that were assessed included: total nucleated cell (TNC) count, antigen presenting cell (APC) count (large CD54+ cells), and APC activation (upregulation of CD54; a measure of product potency). Results: As of May 2013, 1254 subjects were enrolled and have completed treatment. Of these, 278 (20%) pts were ≥80 yrs-old. Disease and infused product characteristics in pts ≥80 yrs vs. <80 yrs are detailed in the table below. Product parameters appear similar between groups. Conclusions: In this large cohort of elderly pts ≥80 yrs treated prospectively with sipuleucel-T immunotherapy, we demonstrate that product parameters were similar to their younger counterparts (<80 years). This implies adequate immune up-regulation in elderly pts. Additional follow-up is needed to explore correlations between OS and various immune parameters in both groups. Clinical trial information: NCT01306890. [Table: see text]