Immunotherapy for metastatic prostate cancer

Chemotherapy with docetaxel is the standard treatment for men with metastatic prostate cancer, and results in statistically significant improvements in survival, as well as in quality of life. However, the response rate to single-agent docetaxel is approximately 40% to 45%, emphasizing a need for alternative approaches. More significantly, with the onset of early, PSA-based detection of prostate cancer and closer follow-up, many men present with metastatic disease that remains asymptomatic. For such patients, the side effects of chemotherapy would compromise their current performance status and, thus, a nontoxic, early treatment option that could improve overall survival would be highly desirable. Immunotherapy represents one such approach; a number of clinical trials have suggested a survival benefit for immunotherapy in metastatic prostate cancer and confirmed that these agents are generally well-tolerated. As is the case for chemotherapy, it is doubtful that maximal survival benefit will be achieved with single-agent immunotherapy; experimental treatments in which mechanistically distinct immunotherapy approaches are combined, as well as approaches in which immunotherapy is combined with chemotherapy or hormonal therapy are currently under investigation. This review will discuss the mechanisms of action of several immunotherapy approaches for metastatic prostate cancer, focusing on active immunotherapy as opposed to administration of anti-tumor antibodies. The relative advantages and disadvantages of current approaches will be noted, and ongoing clinical trials will be highlighted.