Immunotherapy for Prostate Cancer
The advent of precision medicine has ushered in a new way of battling cancer. With an understanding of the genetics of cancer, treatment is now personalized specific to a patient's unique tumor characteristics. However, one of the limitations of precision medicine is the inevitable development of treatment resistance by the tumor. The vast majority of patients, after experiencing clinical benefit, will require a change in treatment as their tumor mutates. As a cancer changes, so must our response. In this perennial "cat and mouse" game, new approaches must be developed to keep up.
Instead of always playing "catch up" with a tumor, immunotherapy offers the greatest hope in our search for a cancer cure. By harnessing the power of the immune system, the body can keep up with new mutations.
What is cancer immunotherapy?
Immunotherapy can be broken into 3 major categories: monoclonal antibodies, vaccines and nonspecific immunotherapies. Antibodies are the body’s ammunition against cancer. In the lab, antibodies can be produced specific to a patient’s tumor. These are then injected into a patient.
Vaccines are also a promising area of research. Already we have effective vaccines against some cancers. There are vaccines for HPV, which protects against cervical cancer, and hepatitis B, which protects against liver cancer. Vaccines are also being developed to treat cancer.
Finally, nonspecific immunotherapies are one of the hottest areas in cancer research currently. These can be divided into:
Cytokines – These are molecules which stimulate the immune system.
Checkpoint inhibitors – These release the brakes on the immune system, i.e. PD-1/PD-L1 PARP inhibitors.
Immunomodulating drugs – Cause a boost to the immune system, i.e. Thalidomide
Immunotherapy for prostate cancer
Prostate cancer is one of the first cancers to benefit from immunotherapy. There are five major categories in use or clinical trials for prostate cancer: therapeutic vaccines, oncolytic virus therapies, checkpoint inhibitors, adoptive cell therapies and adjuvant immunotherapies.
An example of a therapeutic vaccine is Provenge. Provenge is indicated in patients with advanced cancer, that which has spread/metastasized to other parts of the body, and who have few or no symptoms. Other vaccines are in clinical trials.
Oncolytic virus vaccines use a virus to destroy cancer cells and stimulate an immune response by the body against the tumor. Examples are currently being tested.
Checkpoint inhibitors in use include ipilimumab (an antibody) in combination with other therapies.
Adoptive cell therapy is also showing promise in prostate cancer. This involves removing T cells from the patient, modifying them to stimulate a more vigorous immune response then re-infused into the patient.
Other adjuvant immuntherapies include substances that enhance the immune response. Again, these are often used in combination with other therapies.
In summary, as cancer comes from within, it is ironic that the ultimate cure may also come from within.