Harness the immune system to fight colon cancer

Colorectal cancer is the third most common cancer diagnosed in both men and women in the United States.

The American Cancer Society estimates that almost 101,420 new cases of colon cancer will be diagnosed in 2019.

While chemotherapy is still used to prevent recurrence of early stage colon cancer and treatment of advanced/metastatic colon cancer, immunotherapy is playing an increasing role in the treatment for certain group of patients.

Immunotherapy targets medications that utilize a person’s immune system to better recognize and destroy cancer cells. It can treat some people with advanced colorectal cancer as well as certain other cancers that respond to manipulation of the immune system.

Getting past the checkpoints

An important part of the immune system is its ability to keep itself from attacking the body’s normal cells. To do this, it uses “checkpoint” proteins on immune cells, which act like switches that turn on or off to start an immune response. Certain cancers use these checkpoints to keep the immune system from attacking them. New immunotherapy agents that target these checkpoints hold a lot of promise as cancer treatments.

Drugs called checkpoint inhibitors can help people whose colorectal cancer cells have tested positive for specific gene changes, such as a high level of microsatellite instability (MSI-H) or changes in one of the mismatch repair (MMR) genes. Doctors use these drugs for patients whose cancer is still growing after treatment with chemotherapy. They might also be used to treat people whose cancer can’t be removed with surgery, has come back after treatment or has spread to other parts of the body (metastasized).

These drugs are effective mostly in those whose tumors test positive for MSI-H. Researchers are also testing checkpoint inhibitors in clinical trials in combination with chemotherapy for treatment of patients with stage III colon cancer that is MSI-H following surgery to prevent recurrence.

Keeping an eye on side effects

Pembrolizumab (Keytruda) and Nivolumab (Opdivo) are examples of checkpoint inhibitors that target PD-1, a protein on immune system cells called T cells that normally help keep these cells from attacking other cells in the body. By blocking PD-1, these drugs boost the immune response against cancer cells. Doctors give these drugs as an intravenous infusion every 2-3 weeks.

Even though checkpoint inhibitors can be effective and are an exciting treatment option for those suffering from colon and certain other cancers, serious side effects can occur. These drugs work by basically removing the brakes from the body’s immune system. Sometimes the immune system starts attacking other parts of the body, which can cause serious or even life-threatening problems in the lungs, intestines, liver, hormone-making glands, kidneys or other organs. Therefore, we closely monitor these side effects during clinic visits via physical exam and lab assessment.

John Muir Hospital is participating in clinical trials to see if these checkpoint inhibitors can be used in combination with chemotherapy in early stage disease (stage III) following surgery to prevent recurrence and in advanced stage (stage IV) to see if these drugs can be used early in the course of the treatment, either by themselves or in combination with chemotherapy.

Dr. Jewel Johl is a board certified medical oncologist with Diablo Valley Oncology & Hematology Medical Group.

Dr. Jewel Johl