Recent phase III trial results have demonstrated the effectiveness of
sipuleucel-T, a therapeutic
cancer vaccine, in the treatment of metastatic
prostate cancer. Yet, despite the survival benefit of
sipuleucel-T, questions remain about how immunologic agents can be used in the treatment of metastatic
prostate cancer. The primary issue confounding researchers and practitioners about the benefits of
sipuleucel-T is the lack of effect on time to progression. It may be helpful to note that recent phase II data from a different therapeutic
prostate cancer vaccine (
Prostvac), as well as phase III data from an anti-cytotoxic T-lymphocyte antigen-4 (CTLA-4) blocking agent in metastatic
melanoma, also show improved survival without short-term changes in
disease progression. Furthermore, mathematical
tumor growth models provide some insight into the fact that immunologic
therapies do allow for continued
tumor growth, but at a slower rate, thus prolonging survival. This understanding can help to clarify the role of the newly approved
sipuleucel-T in the treatment of metastatic
prostate cancer. It is also possible that appropriate sequencing of
therapies could further improve the
clinical course for such patients. Additional clinical trials will further our understanding of the role of therapeutic
cancer vaccines and add new agents to the armamentarium of
therapy for patients with
prostate cancer.