Exploratory FDG PET/CT Imaging in mCRPC Patients Treated with Sipuleucel-T ± IL-7: A Phase II Trial Subanalysis

Immunotherapy has shown limited efficacy in metastatic castration-resistant prostate cancer (mCRPC), highlighting the need for noninvasive tools to monitor treatment-related biological changes. This case series evaluated exploratory metabolic imaging correlates using 18F-FDG PET/CT in mCRPC patients enrolled in a Cancer Immunotherapy Trials Network (CITN) trial of sipuleucel-T (sip-T) with or without recombinant interleukin-7 (IL-7). Among 54 enrolled patients (NCT01881867), three underwent serial 18F-FDG PET/CT imaging at baseline and following sip-T therapy. Imaging assessed tumor metabolic activity and potential immune-related metabolic changes, based on the premise that immune processes may influence FDG uptake. Patient 1, treated with sip-T alone, demonstrated progressive sternal metastasis with stable SUVmax and marked increases in metabolic tumor volume (MTV: 10.1–34.5) and total lesion glycolysis (TLG: 43.4–145.8), consistent with poor prognosis. Patient 2 showed minimal tumor avidity but transient increases in splenic SUVmax and SUVmean following sip-T, which may reflect treatment-related or immune-associated metabolic activity. Patient 3, treated with sip-T plus IL-7, demonstrated a 33% reduction in SUVmax, stable disease on follow-up imaging, decreased PSA levels, and metabolic changes consistent with treatment response in this individual case. These findings were observed in a single patient and are considered exploratory and hypothesis-generating only. 18F-FDG PET/CT imaging may provide exploratory insights into metabolic changes in tumors and immune-related organs in mCRPC. Metabolic changes in tumors and immune organs may provide insights into treatment-associated biological effects. Larger studies are warranted to validate these findings.