Until recently, cancer treatment was limited to three options-surgery, chemotherapy and/or radiation.
Now: Cancer vaccines are a promising new treatment for virtually all types of malignancies.
To find out more, we spoke with Dr. Michael Morse, a medical oncologist and leading authority on cancer vaccines...
Is the idea of cancer vaccines new? Not at all In the 1700s, it was observed that people who had tumors occasionally improved after they experienced an infection. Then, more than a century ago, a New York surgeon named William Coley identified a patient who had an incurable sarcoma (cancer of the bone, muscle or other supportive tissue) but who experienced a significant reduction of the sarcoma after contracting a skin infection.
Coley then tried treating some patients by injecting them-and their tumors-with a fluid in which two types of bacteria were grown. This was called Coley toxin, which artificially induced inflammation in cancer patients and resulted in an improvement in 40% of patients and a cure in 10%. This treatment, nonspecific immunotherapy, activates the immune system in a general way.
In the last 20 years, immunotherapy for cancer, using vaccines to activate the immune system in a specific way, has become an important field of cancer research.
How do cancer vaccines work? Cancer vaccines aren't like vaccines for viral diseases, such as influenza. Although they don't currently prevent cancel we do hope that one day they will. Rather, they use various methods to stimulate the cells of the immune system to attack cancer cells.
A cancer vaccine uses an antigen, a protein based derivative from a tumor. Once inside the body, the antigen is taken up by dendritic cells, sentinel-like immune cells that break up the antigen and represent it in a form that T-cells can recognize. These T-cells are stimulated by the dendritic cells to then divide into large numbers and to acquire the capacity to recognize and destroy harmful tumor cells.
Our goal is to trigger the immune system to produce an abundance of these "smart" T-cells that can work to eliminate the malignancy.
What kinds of cancer can vaccines fight? Virtually every type of cancer has been studied in a clinical trial, including brain cancer. Many of these trials have involved patients whose cancer has metastasized, or spread to other parts of the body.
Vaccines are also being used in adjuvant settings-in a person who has had a tumor and has a high risk of a recurrence. For example, a patient who has been surgically treated for breast cancer may subsequently receive chemotherapy, hormonal therapy and, a cancer vaccine in a clinical trial to discover whether immunotherapy helps make the other two treatments more successful in preventing a recurrence. Many of these adjuvant studies are focused on melanoma, a deadly skin cancer, because it is thought to be more susceptible to the immune system's attack.
How successful are cancer vaccines? Studies show that 3% to 5% of solid tumors, such as those found in the lung, breast or prostate, shrink after using a cancer vaccine. In nonsolid, or hematological, cancers, such as leukemias and lymphomas, the response rate is slightly higher, because of the unique antigens in these types of cancers.
These success rates may sound low, but there's reason to be optimistic. Many studies report that a patient whose immune system is successfully activated by the vaccine either lives longer or experiences slower growth of the cancer than someone whose immune system is not successfully activated.
A recent study of the vaccine Theratope, used for breast cancer, did not show a positive result overall but it did show a benefit in a subgroup of women who were on hormone therapy, mostly the drug tamoxifen (Nolvadex). The median overall survival for patients on hormone therapy who also received Theratope was 36.5 months, compared with 30.7 months for those who also received the control vaccine. Further clinical trials will focus on the effectiveness of cancer vaccines in these and other subgroups. Before long, we may learn the best way to give dozens of specifically targeted vaccines to help many kinds of patients.
Researchers also have reason for cautious optimism because these vaccines do work-they generate T-cells that recognize and fight cancer. Before cancer vaccinations, there were fewer such T-cells. Even when tumors do not significantly shrink, cancer patients who have an immune response to vaccines have had longer periods before the cancer worsened and they survived longer than the non-vaccine patients.
Are cancer vaccines toxic? No, not in the way that chemotherapy can be toxic. Using a vaccine to stimulate the immune system might be thought of as a "natural" way to treat cancer. It does not have the same side effects as those caused by chemotherapy and radiation, but it can cause fevers, allergic reactions and autoimmune disorders. Cancer patients consider vaccines nontoxic, and that's one reason why they are so excited about the prospect of this treatment.
How can people who have cancer find out about the availability of the vaccines? Cancer vaccines are being tested but are not yet available as part of the standard treatment regimen offered by cancer specialists.
However there are more than 150 ongoing clinical trials involving cancer vaccines. Talk to your oncologist about cancer vaccines to see if this treatment might be available and right for you.
