Cancer originates from the body’s own cells and the immune system may, therefore, not be able to recognize cancer cells as foreign invaders to the same extent it does with viruses or bacteria. As a result, it may not fight cancer to the same extent it fights infections.
Vaccine, or active specific cancer immunotherapy, is an experimental form of treatment that stimulates the immune system to recognize the antigens on cancer cell surfaces as foreign invaders. Cancer vaccines are immunotherapy treatments that seek to stimulate the immune response against cancers in patients who have already developed the cancer. They are injected into the patient either under the skin, or into the blood or lymph system. These are different from vaccines used to prevent infections – cancer vaccines are not given to patients in order to prevent cancer.
It takes time for the body to build up its own defenses, so the beneficial effects of a vaccine may take months to occur. When successful, however, vaccines may promote longer-lasting tumor control or shrinkage than chemotherapy or targeted therapies and may cause fewer side effects than chemotherapy and other forms of immunotherapy such as interferon and interleukin. Unfortunately, only about 5% of patients have clinical tumor shrinkage with current cancer vaccines.
Vaccines Currently Under Investigation Include:
- Imylgic (talimogene laherparepvec “T-Vec” is a new type of vaccine derived from the herpes virus, but it is genetically modified so that it does not cause a viral infection. This vaccine is injected into the tumor, and after injection the virus is able to divide only in tumor cells causing their death. The activated immune system can then fight other tumors in the body that have not been injected. A large phase III study demonstrated a durable response rate, and studies combining Imylgic with Keytruda, Opdivio, or Yervoy have shown promising results.
- PV10 is an investigational drug containing rose bengal, and is injected into cutaneous melanoma tumors. It is a phase II study of 80 patients both injected and non-injected tumors shrank. There is currently an ongoing phase III clinical trial comparing PV10 to chemotherapy or Imylgic in patients who are not candidates for targeted therapy or immunotherapy.