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Updated on August 20, 2025
Colorectal cancer is cancer that begins in the large intestine, the lower portion of the GI tract that consists of the colon and rectum. This type of cancer may also be called colon cancer or rectal cancer, depending on which part of the large intestine that the cancer begins. It is the third most common type of cancer in the United States.
Most colorectal cancers begin with abnormal growths called polyps. These growths form on the inner lining of the large intestine. In most cases, polyps are benign (non-cancerous) but become cancerous over time. Certain types of polyps and polyps that are larger in size are more likely to become cancerous.
Colorectal cancer typically occurs after age 50, but it can occur at younger ages. The number of people under age 50 who are diagnosed with colorectal cancer has risen significantly in recent decades. The reasons for this are not fully understood, though genetics and family history appear to play a role.
Treatment for colorectal cancer
Treatment for colorectal cancer depends on multiple factors, including the location and size of the cancer, the stage, and the results of molecular testing. A treatment plan may include a combination of the following.
- Surgery to remove segments of the large intestine affected by tumors.
- Ablation, a procedure that destroys tumors with energy waves or other methods.
- Radiation therapy, used mostly for rectal cancer.
- Chemotherapy, which can be used before surgery, after surgery, or as a main treatment for advanced cancers. Chemotherapy may be systemic (acting on cancer throughout the body) or regional (focused on the specific part of the body with cancer).
- Targeted therapy, the use of precision medicine drugs to target specific proteins cancer cells use to grow.
- Immunotherapies, which help the immune system detect and destroy cancer cells.
What types of immunotherapies treat colorectal cancer?
The immunotherapies used for the treatment of colorectal cancer are called immune checkpoint inhibitors.
Immune checkpoints are proteins that prevent the immune system from attacking cells. Immune checkpoints are found on healthy cells throughout the body. Some cancer cells produce large amounts of immune checkpoints, which help the cancer avoid detection by the immune system—basically, they act as a disguise.
Immune checkpoint inhibitors block or disable specific immune checkpoints. This removes the disguise, helping the immune system to recognize the cancer cells for what they are—diseased cells that should be eliminated.
When are immunotherapies used to treat colorectal cancer?
Immunotherapy can be a treatment option for early-stage and advanced-stage colorectal cancers that have tested positive for specific gene changes called microsatellite instability (MSI) and changes in mismatch repair (MMR) genes.
These changes cause large numbers of errors in the DNA inside cancer cells, and result in the production of large numbers of abnormal proteins called neoantigens.
If drugs like immune checkpoint inhibitors can disable immune checkpoints, neoantigens provide a good target for the immune system as it attacks cancer cells.
What are subcutaneous immunotherapies?
Most immune checkpoint inhibitors are administered with an intravenous (IV) infusion, where the drug is delivered directly into the bloodstream through a needle inserted into a vein.
Subcutaneous immunotherapies are a new and emerging treatment. Instead of being delivered into the bloodstream, these medications are injected into a layer of tissue called the subcutaneous layer, located just below the skin. While the number of immunotherapies available as subcutaneous administration is limited, it is expected to expand in the future.
Subcutaneous infusions are typically given in the abdomen or thigh, but instructions for administration can vary depending on the drug. The route of administration does not change how a drug works or its effectiveness.
Appointments for subcutaneous immunotherapy injections offer more flexibility for patients, caregivers, and healthcare providers. While an intravenous infusion requires a visit to an infusion center or hospital, a subcutaneous injection can be administered at a healthcare provider’s office. Appointments are also shorter—a subcutaneous injection takes a few minutes, while an IV infusion can take 30 to 90 minutes.
Remember that there is no best treatment option for colorectal cancer. Different treatments work better for different people, and your best source of information about treatment options will always be your healthcare provider.
