Sipuleucel-T plus IL-7 linked to 33% SUVmax reduction in one mCRPC patient via FDG PET/CT

Immunotherapy has shown limited efficacy in metastatic castration-resistant prostate cancer (mCRPC), a challenging disease where standard treatments often fail. There's a critical need for noninvasive tools to monitor treatment-related biological changes, beyond traditional markers like PSA, to better assess therapeutic response. [18F]-FDG PET/CT imaging, which measures glucose metabolism, offers a potential avenue to evaluate both tumor metabolic activity and immune-related metabolic shifts, as immune processes can significantly influence FDG uptake. This approach could provide earlier insights into treatment effectiveness or resistance in mCRPC.

This case series subanalysis evaluated [18F]-FDG PET/CT imaging correlates in three mCRPC patients drawn from a larger Cancer Immunotherapy Trials Network (CITN) trial (NCT01881867) of Sipuleucel-T with or without recombinant interleukin-7 (IL-7). Patients underwent serial [18F]-FDG PET/CT imaging at baseline and post-therapy. The primary endpoints included assessing changes in tumor metabolic activity, specifically SUVmax, metabolic tumor volume (MTV), and total lesion glycolysis (TLG), as well as potential immune-related metabolic changes in organs like the spleen. This exploratory approach aimed to identify noninvasive biomarkers of treatment response.

Patient 1, treated with Sipuleucel-T alone, exhibited progressive sternal metastasis with stable SUVmax but marked increases in MTV from 10.1 to 34.5 and TLG from 43.4 to 145.8, consistent with a poor prognosis. Patient 2 showed minimal tumor avidity but transient increases in splenic SUVmax and SUVmean following Sipuleucel-T, potentially reflecting immune-associated metabolic activity. The most notable finding came from Patient 3, who received Sipuleucel-T plus IL-7. This patient demonstrated a 33% reduction in SUVmax, stable disease on follow-up imaging, and decreased PSA levels. These metabolic changes were consistent with a positive treatment response in this individual case. While these findings are exploratory and hypothesis-generating, they suggest that [18F]-FDG PET/CT imaging may offer valuable insights into treatment-associated biological effects in both tumors and immune-related organs.

Patient 3, treated with Sipuleucel-T plus IL-7, demonstrated a 33% reduction in SUVmax, stable disease on follow-up imaging, and decreased PSA levels, indicating a positive metabolic response.