Colorectal cancer is the third most commonly diagnosed cancer in the U.S. and the third leading cause of cancer death. This year, the American Cancer Society estimates 147,500 new cases will be diagnosed in the U.S. and more than 57,000 will die from it.
Colon cancer can occur at any age, but is most commonly diagnosed after 40. Someone with a parent or sibling with the cancer has twice the risk of also developing the disease. Some other risk factors include: personal history of colorectal cancer (even after successful treatment, new cancers can develop in other areas of the colon and rectum), history of polyps, chronic inflammatory bowel disease, a high-fat diet mostly from animal sources, physical inactivity, obesity, and smoking.
Developing a Colorectal Cancer Vaccine
Normally, the immune system responds to proteins found on the surface of cells – seeking out foreign proteins and mobilizing an attack if they are found. Cancer cells are mutations of the body's own cells, and thus, the body often doesn't recognize them as "foreign". The challenge for researchers is to find a way for the body to target the cancer cells without attacking normal cells.
Doctors are now testing a vaccine that will hopefully increase the body's ability to recognize and naturally fight cancer cells. It's called ALVAC-CEA/B7.1. The vaccine is incorporated into a canarypox virus. This is a bird virus that can infect human cells, but won't grow or divide –so it won't cause active infection. Once the vaccine is inside a cell, it causes the cell to temporarily display elevated levels of carcinoembryonic antigen, or CEA, a protein that's overexpressed in 95 percent of colorectal cancer cells. Hopefully, the immune system will learn the CEA is a foreign substance and attack it (and eventually, the cancer cells).
Currently, the ALVAC-CEA/B7.1 vaccine is being tested in up to 90 patients with metastatic colorectal cancer. Participants will be randomized into one of three groups. The first group will get the vaccine once a week for three weeks prior to starting standard chemotherapy. They will also receive a vaccination at the beginning of each chemotherapy cycle, for a total of seven vaccinations. The second group will get the same regimen as the first group, plus doses of tetanus toxoid prior to each chemotherapy cycle. This will help researchers determine whether the tetanus toxoid enhances the body's immune response to the vaccine. The third group will receive standard chemotherapy. Those who respond after four chemo cycles (partial or complete disappearance of the tumor) will have the option of getting four doses of the vaccine.
Phase I studies show promise. In a small group of patients with advanced cancer, those who responded to the vaccine had a 60 percent greater two-year survival rate than non-responders (no immune response). The ALVAC-CEA/B7.1 vaccine is currently in the beginning of Phase II trials and is being tested in the following U.S. cities: