Posted: Jan 03, 2018
This month, Prostatepedia is talking about immunotherapy for prostate cancer.
Dr. Charles “Snuffy” Myers offers his thoughts on this month’s conversations.
Every January we publish an issue on immunotherapy. If you compare our January 2017 issue with this year’s conversations, I am sure the advances in the science behind immunotherapy will excite you. While we only have one FDA-approved immunotherapy called Provenge (sipuleucel-T), the future looks promising.
As Dr. Tomasz Beer points out in his conversation, we’re at an interesting intermediate stage in immunotherapy development. We know that various immunotherapy approaches like vaccines, checkpoint inhibitors, and CAR T-cell treatments can control a variety of cancers, but we don’t yet have an immune-based treatment that has a consistent, major impact on prostate cancer survival or even quality of life.
I’d like to highlight several important themes in this issue. First, evidence continues to suggest a favorable interaction between hormonal therapy and various forms of immunotherapy. Second, there is continued interest in combining immunotherapy with radiation therapy. This offers the hope that immunotherapy might open the door for more effective multimodality treatment.
The emergence of CAR T-cell treatment for leukemia and lymphoma has been very exciting; patients with very advanced disease are entering remission. It will be interesting to see this approach applied to prostate cancer. Also note that major funding for CAR T-cell trials in prostate cancer comes from the Prostate Cancer Foundation (PCF), a nonprofit, and not the United States government. This is a trend I noted last month.
There have been some notable disappointments. The randomized trial testing the Prostvac vaccine failed to meet the requirements for FDA approval. It is still possible that this vaccine might prove valuable in patients with less advanced prostate cancer.
Also, the available checkpoint inhibitors continue to show only modest activity. It may well be that CTLA-4 and PD-L1, the two checkpoint proteins currently targeted, are not the only checkpoint proteins produced by prostate cancer.
For example, earlier this year, investigators from MD Anderson Cancer Center showed that Yervoy (ipilimumab), an agent that targets CTLA-4, triggers production of another checkpoint protein called VISTA. It may well be that prostate cancer can block immune response in a variety of ways and that we need to inactivate each of these defenses.
Even with these difficulties, immunotherapy offers potential benefits that warrant the attention it is receiving.
One of the benefits is that the immune response can evolve over time to match the evolution of the cancer cell population’s resistance. In the laboratory, immunotherapy also offers one of the most robust means of attaining durable and complete remissions.