Background: Sip-T is an FDA-approved, autologous cellular immunotherapy for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). Post-hoc analysis of the phase 3 IMPACT study revealed that compared with the highest baseline PSA quartile, patients (pts) in the lowest quartile treated with sip-T had a larger overall survival (OS) benefit, suggesting sip-T is most beneficial if administered earlier in the treatment of mCRPC (Schellhammer et al., Urology. 2013.). This analysis evaluated pt characteristics by PSA quartiles in PROCEED (NCT01306890). Methods: Pts enrolled in PROCEED with baseline PSA and ≥ 1 sip-T infusion were included in this analysis. PSA values were divided into quartiles, and trends in baseline pt characteristics were evaluated as well as time to first anticancer intervention (tACI) with approved mCRPC therapies (docetaxel [D], cabazitaxel, abiraterone [abi], or enzalutamide [enz]) following sip-T treatment. Radium-223 was approved too late in the conduct of PROCEED to be included in the tACI analysis. Results: PSA quartiles from 1880 eligible PROCEED pts were lower than those of IMPACT (Table). Pts in the highest PROCEED quartile were older, more likely to have ECOG performance status ≥ 1, > 10 bone metastases, visceral metastases, and higher ALP and LDH, and lower hemoglobin compared with the lowest PROCEED quartile. More African American men and greater prior systemic therapy use were observed in the highest PSA quartile. Following sip-T, the median tACI (11.0, 8.2, 7.6, and 6.6 mos) was inversely proportional to PSA quartile. Conclusions: Lower baseline PSA values in PROCEED relative to IMPACT suggest that in a real-world setting, clinicians are using sip-T earlier in the treatment of mCRPC. Pts in the lowest PSA quartile had the best prognostic features and longest tACI. Additional patient follow-up is ongoing to evaluate OS and survival by quartile from PROCEED. Clinical trial information: NCT01306890