Abstract
Following FDA approval of sipuleucel-T in 2010 for metastatic castration resistant prostate cancer (mCRPC), several studies have described the effect of sipuleucel-T on peripheral immune responses. Retrospective associations have also been made with immune responses and survival. A recently published study by Fong et al. was the first to characterize the immune response of sipuleucel-T in the tumor microenvironment. The findings of this study have been hypothesis generating, yet it remains unclear whether the peri-tumor immune response described is predictive of survival. Increasing evidence suggests that radiographic or PSA progression does not accurately reflect survival with sipuleucel-T and other immunotherapies. Finding an immune biomarker which can accurately reflect clinical benefit and validating it prospectively offers the potential for a predictive indicator of response in an area where none currently exists.