Immunotherapy is a cancer treatment that utilizes a patient’s own immune system to combat the disease. For individuals with colon cancer, this approach has become a meaningful option, though its effectiveness is specific to certain patients. Immunotherapy functions by enhancing the body’s natural defenses, enabling them to recognize and target cancer cells more effectively. This method has shown particular promise in treating a subset of colon cancers.
How Immunotherapy Works Against Colon Cancer
The human immune system has T-cells, a type of white blood cell that can identify and destroy unhealthy cells, including cancerous ones. T-cells constantly patrol the body for signs of disease. Cancer cells, however, can be deceptive and develop mechanisms to evade this immune surveillance. They produce proteins on their surface that act as “stop signs” or “brakes” for the immune system, which interact with checkpoints on T-cells, telling them to stand down. This allows the tumor to grow unchecked.
Immunotherapy for colon cancer works by interfering with this process. The most common form of this treatment uses drugs that block the interaction between the cancer cells and the T-cells. By blocking these “stop signs,” the treatment releases the brakes on the immune system. This action allows the T-cells to properly recognize the cancerous cells as a threat and mount an attack to destroy them.
Determining Candidacy for Treatment
Not all individuals with colon cancer are suitable candidates for immunotherapy. The treatment’s effectiveness is closely linked to the specific genetic characteristics of the tumor. A detailed analysis of the tumor tissue is performed to identify biomarkers that predict whether a patient is likely to respond.
The two most important biomarkers for determining eligibility are Microsatellite Instability-High (MSI-H) and Mismatch Repair Deficiency (dMMR). Both markers indicate a flaw in the cancer cell’s ability to repair errors that occur during DNA replication. The mismatch repair (MMR) system is like a “spell-checker” that corrects mistakes when DNA is copied. When this system is deficient (dMMR), errors accumulate.
This high number of errors leads to microsatellite instability. These numerous mutations cause the cancer cells to produce many abnormal proteins, which makes them look very different from healthy cells. This high degree of abnormality makes the tumor highly visible to the immune system. Consequently, patients whose tumors are classified as MSI-H or dMMR are often excellent candidates for immunotherapy.
Types of Immunotherapy Used
For colon cancer, the primary class of immunotherapy drugs used is immune checkpoint inhibitors. These medications are designed to block the proteins that cancer cells use to suppress the immune system. The main targets for these drugs are proteins called PD-1, PD-L1, and CTLA-4.
FDA-approved checkpoint inhibitors for treating MSI-H/dMMR colon cancer include Pembrolizumab (Keytruda) and Nivolumab (Opdivo). Both drugs work by blocking the PD-1 protein, preventing cancer cells from deactivating T-cells. These medications are often used as a first-line treatment for metastatic colon cancer with these specific biomarkers.
Another checkpoint inhibitor, Ipilimumab (Yervoy), may be used in combination with Nivolumab. Ipilimumab targets a different checkpoint protein known as CTLA-4, which also serves as a brake on T-cells. By blocking both PD-1 and CTLA-4, this combination therapy can produce a more robust immune response against the cancer.
Potential Side Effects and Management
Because immunotherapy stimulates the entire immune system, it can sometimes lead to the immune system attacking healthy cells and tissues in the body. These reactions are known as immune-related adverse events. The side effects can affect various parts of the body and range from mild to severe. It is important for patients to communicate promptly with their healthcare team.
Common side effects include:
- Skin reactions, such as rash and itching.
- Gastrointestinal issues, leading to diarrhea or colitis (inflammation of the colon).
- Problems with endocrine glands, such as the thyroid, leading to hypothyroidism or hyperthyroidism.
- Inflammation of the lungs (pneumonitis), which can cause shortness of breath or a cough.
The management of these side effects is a key part of the treatment process. Patients are instructed to report any new or worsening symptoms to their oncology team immediately. Early detection and intervention are important for preventing more serious complications. For many of these side effects, treatment with corticosteroid medications can help to suppress the overactive immune response and resolve the symptoms.
Treatment Administration and What to Expect
Immunotherapy for colon cancer is administered in an outpatient setting as an intravenous (IV) infusion. The medication is delivered directly into a vein through a small needle and tubing. This process takes place in a specialized clinic or infusion center under the supervision of medical professionals.
The frequency of treatment sessions depends on the specific drug regimen being used. Some infusions are scheduled every three weeks, while others may be administered every six weeks. The infusion itself can last from 30 to 90 minutes.
On a treatment day, a nurse will place an IV line, usually in the patient’s arm. After the immunotherapy drug is slowly infused, there is a short observation period to monitor for any immediate reactions. The healthcare team will check vital signs and ensure the patient is feeling well before they are cleared to leave.