Colorectal Cancer: Key Q & A

Reviewed By:
Martin E. Liebling, M.D., FACP

What is colorectal cancer?

Colorectal cancer is a type of cancer that involves uncontrolled growth of abnormal cells in the colon or rectum. The colon and rectum make up the last sections of the gastrointestinal system.

Colorectal cancer starts in the inner lining of the colon or rectum, usually as abnormal growths called polyps. Polyps may remain benign, but some are precancerous and over the years turn malignant. The polyps most likely to turn cancerous are adenomatous polyps, or adenomas. The adenomatous cells are gland cells on the inner lining of the colorectal tract.

Colorectal cancer can spread from the innermost mucosal layer to the wall of the colorectal tract and beyond. Cancer in the colorectal wall can grow into the blood vessels or lymph vessels. These vessels can allow the cancer to spread to distant parts of the body.

How dangerous is colorectal cancer?

Colorectal cancer is the second deadliest form of cancer in the United States. However, the mortality rate has been dropping for the past 15 years, which is most likely due to improved screening and treatment methods.

The outlook is best when cancer is confined to the innermost layer and does not block or perforate the large intestine. This occurs in the early stages of the cancer. Ninety percent of people treated for early-stage colorectal cancer, before it begins to spread, survive at least five years and often much longer, according to the American Cancer Society.

However, only 39 percent of colorectal cancer is caught early. The five-year survival rate declines to 68 percent when colorectal cancer spreads to nearby organs or lymph nodes and 10 percent when colorectal cancer spreads to distant organs or lymph nodes.

What does screening for colorectal cancer involve?

The U.S. Centers for Disease Control and Prevention recommends a screening schedule for adults age 50 and older that includes a fecal occult blood test or a fecal immunochemical test once every year. In addition, a flexible sigmoidoscopy or double-contrast barium enema every five years or a colonoscopy every 10 years should also be performed. If you have a higher risk of colorectal cancers, such as a family history of colorectal cancer, you should start screening at a younger age and you may need testing more often. For example, the American Cancer Society recommends that people with a condition called familial adenomatous polyposis begin colonoscopy during their teens.

How is the severity of colorectal cancer described?

The most common way of describing the severity of, or staging, colorectal cancer is the American Joint Committee on Cancer's TNM system. It includes information about the tumor, any involvement of lymph nodes and any metastasis, or spread to other parts of the body.

Stage 0 is also called carcinoma in situ. This occurs when cancer is found in only the innermost lining of the colon, rectum, or both. It is the least severe form of colorectal cancer.

Stage I occurs when the cancer has spread beyond the innermost lining of the colon or rectum to the second and third layers and involves the inside wall, but it has not spread to the outer wall or outside the colon or rectum.

Stage II occurs when the cancer has spread outside the colon or rectum to nearby tissue, but it has not gone into the lymph nodes.

Stage III occurs when tumor cells have spread to lymph nodes near the colon or rectum.

Finally, stage IV colorectal cancer occurs when the cancer may have spread to nearby lymph nodes and has spread to other parts of the body, such as the liver or lungs.

Are there different types of colorectal cancer?

Yes. More than 95 percent of colorectal cancers are adenocarcinoma, which is cancer of the gland cells that line the inside wall of the colon and rectum. These usually develop from adenomatous polyps, which are also called adenomas. These are abnormal precancerous growths that can form in the inner lining of the colon and rectum. Some adenomatous polyps and other kinds of polyps, such as inflammatory polyps, remain benign.

Uncommon types of colorectal cancer include carcinoid tumor, gastrointestinal stromal tumor and lymphoma. Carcinoid tumor develops from the colon's hormone-producing cells. Gastrointestinal stromal tumor develops in the colon wall from specialized cells called interstitial cells of Cajal. Lymphomas are cancers of the immune system that usually start in lymph nodes.

How is colorectal cancer treated?

There are multiple ways to treat colorectal cancer. The treatment options that are right for you generally depend on how far the cancer has progressed, your age, and your overall health. Surgical removal of the cancer is the most common treatment for all stages of colorectal cancer.

Radiation therapy may be performed to reduce large cancers before surgery, to kill any cancer cells left after surgery, or to reduce pain, intestinal blockage or other symptoms. It uses x-rays or other forms of radiation to kill cancer cells. Side effects include sexual problems, diarrhea, nausea and fatigue and are usually temporary.

More frequently, chemotherapy may be used for the same reasons as radiation therapy including reducing the tumor burden before surgery, killing remaining cancer cells after surgery and easing symptoms. It is the use of drugs to kill or control cancer cells. Chemotherapy may be combined with radiation therapy in treatment.