Dr. Tomasz Beer, the Deputy Director of the Oregon Health & Science University Knight Cancer Institute, specializes in prostate cancer oncology. Dr. Beer was selected as one of six top scientists to take part in a research dream team that joins together world-class institutions to study treatments for advanced prostate cancer.
Prostatepedia spoke with him recently about immunotherapy for prostate cancer.
What is immunotherapy and how is it used in prostate cancer treatment?
Dr. Beer: Our immune systems are capable of controlling, or maybe even eliminating cancer. Immunotherapy provides some sort of treatment or intervention that helps engage the immune system in that task. There are a number of different ways to do that. While we’ve been working on immunotherapy for several decades, it’s still in its infancy. We don’t have a full and complete understanding of how the immune system works and how to manipulate it to our advantage.
We know enough now that cancer treatments that rely on the immune system continue to become a reality for patients and to make a difference.
We’re in that transition period between preliminary and developing opportunities to deliver reliable treatments.
How does it work? In an antigen-specific approach, we develop a vaccine or some other way to activate the immune system against a particular antigen (a protein made by a cancer cell) that is unique or predominant to the cancer.
Another approach is to activate the immune system more generally, and by doing that, hope that the immune system distinguishes between our own antigens and the cancer’s.
These approaches are therapeutic. These are not the sorts of vaccines that we think of in terms of the prevention of infectious diseases, where we vaccinate ourselves when we’re healthy to build up immunity before an infection. Right now, immunotherapy means treatment for an established cancer.
So then these vaccines don’t prevent cancer: this is a type of treatment.
Dr. Beer: Yes. For example, the vaccine against HPV infections is a conventional antiviral vaccine for a viral infection, and because the virus leads to cervical cancer, it’s also a cancer prevention strategy. That is a different way to use the immune system to fight cancer. Immunotherapy is therapeutic cancer vaccination.
Why are some forms of immunotherapy more effective for different kinds of cancer? What is it about prostate cancer that makes it more susceptible to that kind of approach?
Dr. Beer: First, we don’t have a full understanding of these distinctions. Second, just because there are treatments for one disease and not another doesn’t necessarily mean that prostate cancer is more susceptible.
Dendreon, the company that developed the vaccine for prostate cancer, focused on prostate cancer and did not have the resources or bandwidth to try the same thing for other cancers extensively. It’s sort of an accident of history in the case of Provenge (sipuleucel-T).
That particular vaccine targeted a prostate cancer-specific antigen called PAP, so it wouldn’t have worked in its normal form against other cancers. One could take a similar approach with an antigen that was specific to other tumor types, but it just hasn’t happened yet.
With immune checkpoint inhibitors—the most contemporary form of therapy—we think that some cancers are more susceptible because they have more abnormal antigens. The cancers with higher mutational burden seem to respond better to these agents and it’s probably because they’re more different than normal cancers with pure mutations.
There are also other factors. For instance, melanoma or kidney cancers have traditionally been thought of as more susceptible to immune interventions because there are rare patients whose native immune systems were successful against them. But we don’t know if one cancer is more susceptible to immune therapy than another or for what reason. We’re still learning about that.