Understanding the colon and rectum

The colon and rectum make up the large intestine (also called the large bowel). The colon is a muscular tube that's about 5 feet long. It forms the last part of the digestive tract. It absorbs water and stores food waste. The rectum is the last 6 inches of the large intestine.

The colon and rectum have a smooth inner lining. It is made of millions of cells. These cells replace themselves every day to keep the lining healthy. Changes in these cells can lead to growths in the colon and rectum that can become cancer.

When the colon lining changes

Changes that happen in the cells that line the colon or rectum include:

• Polyps. These are fleshy clumps of tissue that form on the inner lining of the colon or rectum. Small polyps are usually benign (not cancer). But over time, cells in a type of polyp known as an adenomatous polyp (or adenoma) can change and become cancer. The longer a polyp is there and the larger a polyp grows, the more likely it is to become cancer. This happens over a period of years. That's why these growths should be removed when possible. Removing polyps early may prevent cancer from forming. 

• Colorectal cancers. These usually start when polyp cells grow out of control. As cancer grows, it can invade the deeper layers of the colon or rectal wall. Cancer can grow beyond the colon or rectum and into nearby organs as time goes on. It can spread to nearby lymph nodes. The cancer cells can also travel to other parts of the body. This is known as metastasis. The sooner a cancer tumor is removed, the better the chance of keeping it from spreading.

Treatment choices for colon and rectal cancer

You and your healthcare provider will decide on the treatment plan that’s best for your needs. Treatment choices can include:

• Surgery. This is the most common treatment. It's done to remove the cancer in the colon and rectum. Some nearby tissue is also removed. This may include nearby lymph nodes.

• Chemotherapy. This treatment may be done along with surgery. Or it may be done instead of surgery if the cancer has spread. Strong medicines are used to kill cancer cells. This is called systemic therapy. It works throughout the body. Chemotherapy is often done as an outpatient procedure in a healthcare provider's office. It is also done at a clinic or hospital. You may take the medicine as a pill. Or you may get it through an intravenous (IV) infusion. This slowly releases the medicine into your blood.

• Radiation therapy. This treatment may be used for rectal cancer. High-energy X-rays are focused on the tumor to kill cancer cells. It’s known as localized therapy. It targets the cancer and not the whole body. It's usually done on an outpatient basis in a hospital or radiation clinic.

• Targeted therapy. This treatment uses medicines that target certain genes, proteins, or cell functions that help cancer cells grow. Cancer cells are tested to see if they have the changes the medicines target. Sometimes targeted therapy is given along with chemotherapy. It can also be used by itself.

• Immunotherapy. This treatment uses medicines that help the body's immune system attack the cancer. These medicines can be helpful in treating colorectal cancers that have certain gene changes. Immunotherapy might be a choice for advanced colorectal cancers with these changes. It may also be used if chemotherapy hasn't worked.