Correlation of increased eosinophil count following sipuleucel-T treatment with outcome in patients (pts) with metastatic castrate-resistant prostate cancer (mCRPC).

4650 Background: Sipuleucel-T is the first autologous cellular immunotherapy approved for asymptomatic or minimally symptomatic mCRPC. In the IMPACT trial, pts treated with sipuleucel-T had transient increases in eosinophil counts compared with control. In this retrospective analysis, we assess potential correlations between eosinophilia, overall survival (OS), prostate cancer-specific survival (PCSS) and immune response following sipuleucel-T. Methods: Data from three phase III trials (D9901, D9902A, and IMPACT) were pooled. The analysis included CBCs performed at baseline and wks 2–34. Eosinophilia was defined as either >ULN (with normal baseline), or a max change from baseline within the top quartile, at any time between wks 2–16. Results: Increased eosinophil counts were seen in sipuleucel-T pts by wk 6, decreasing to near baseline by wk 14; eosinophil counts in control pts were stable. Of 377 sipuleucel-T pts eligible for analysis, 105 (27.9%) had eosinophilia. Baseline disease characteristics associ...