Immunotherapy Comes of Age in Prostate Cancer:
The Clues Hidden in Failed Prostate Cancer Trials IPCSG Newsletter • Treatment Advances What the “Failures” Are Finally Teaching Us A patient-friendly review of the science — Summer 2026 BLUF (Bottom Line Up Front): For fifteen years, the checkpoint-inhibitor drugs that revolutionized melanoma, lung, and kidney cancer failed one prostate-cancer trial after another — six large Phase 3 studies came back negative. But hidden inside those “failures” was a small group of men who had dramatic, lasting remissions. By studying those rare responders one cell at a time, researchers have now identified why most prostate tumors resist immunotherapy (immune-suppressing “SPP1” macrophages) and what lets a few tumors melt away (unusual killer T-cell populations). Today, only men whose tumors carry specific genetic signatures — mismatch-repair deficiency (dMMR), high microsatellite instability (MSI-H), or high tumor mutational burden (TMB) — have an FD...