Colorectal Cancer


If you have just been told that you have colon or rectal cancer, this guide is a good starting point to help you better understand the disease and your options for treatment. In the pages that follow, you will find information on how colorectal cancer develops, how your doctors will work with you to plan treatment to achieve the best possible outcomes and how to manage symptoms and possible side effects of treatment.

What is colorectal cancer?

Most people discuss colorectal cancer as one type of cancer, but there are important differences between colon and rectal cancer. First, colon cancer is much more common. Second, the treatment of the two types of cancer can differ substantially, as will be discussed later in the guide.

Where does colorectal cancer occur?

The colon and the rectum are major organs in the digestive system, which processes everything you eat and drink. Your digestive system helps to keep those things your body needs, such as vitamins, proteins, water, and so on, and moves the rest as waste material to be eliminated from your body (Figure 1). The colon, also known as the large intestine, is about 6 feet long. The last 6 to 12 inches of the colon make up the rectum and the anal canal. The anal canal ends at the anus, the opening of the large intestine to the outside of the body. Colorectal cancer develops in the inner lining of either the colon or the rectum.

How does colorectal cancer develop?

Most colorectal cancers are thought to start as a polyp, or an abnormal growth in the lining of the colon or rectum. Although the majority of polyps are not cancerous, some develop into colorectal cancer, usually over many years. The risk of a polyp containing cancer cells is related to the type of polyp and its size.

Colorectal cancer can spread beyond the colon or rectum in one of three ways:

  • The tumor can invade directly into the wall of the colon and surrounding tissue.
  • If cancer cells break off from the tumor, the cells can travel through the lymph system to lymph nodes in the area of the tumor.
  • If cancer cells enter small blood vessels, the cells can travel throughout the body via the bloodstream.

Many factors may contribute to the growth of a cancer, but one factor seems to be involved in the development of all cancers — an abnormal change in a gene. This genetic change — also known as a genetic mutation — causes cells to grow and divide rapidly and become a cancerous tumor. Genetic mutations may develop in the cells lining the colon during a person’s lifetime (after birth); these mutations are known as acquired and usually occur when a mistake is made as DNA copies itself during cell division. Colorectal cancer caused by an acquired mutation is known as sporadic cancer; about 70 percent of colorectal cancers are sporadic. The other 30 percent of colorectal cancers are hereditary; that is, they are caused by genetic mutations that people have inherited from their parents.

The two most common forms of hereditary colorectal cancer are hereditary nonpolyposis colorectal cancer (also known as HNPCC or Lynch syndrome) and familial adenomatous polyposis (FAP). Colorectal cancer develops at much younger ages in people with either HNPCC or FAP compared with sporadic cancers (not linked to hereditary mutations). Because of this, if you are younger than 50 years when colorectal cancer is diagnosed, your doctor may suggest genetic counseling and testing for HNPCC or FAP. If you have a genetic mutation, a first-degree relative (a sibling, child, or parent) will have a 1 in 2 chance of also having the mutation. Thus, genetic counseling and testing can help not only you but also other members in your family who may be affected by the hereditary mutation. FAP can become evident at a young age, so this syndrome is one of the few for which genetic testing is done for children. Genetic testing is also important because people with HNPCC or FAP are at greater risk for the development of some other types of cancer, and more frequent screening may be necessary to make sure that if one of these cancers develops, it is detected early.

Who gets colorectal cancer?

Colorectal cancer is the third most common cancer diagnosed in both men and women. Colon cancer occurs slightly more often in women than in men, but rectal cancer occurs more often among men. Because both colon and rectal cancer are caused by multiple genetic mutations that accumulate over many years, colorectal cancer usually develops in people who are over the age of 50. The highest rates for both types of cancer are found in African-American and Caucasian individuals, and the lowest rates, in Asian-American individuals.

Who treats colorectal cancer?

The treatment of colon and rectal cancers requires a team that includes health care professionals from many specialty areas. A gastroenterologist is usually the doctor who is the first to find cancer during a screening colonoscopy or a work-up for symptoms. An operation is the primary treatment and offers the best chance for cure in most cases of colon and rectal cancer. Therefore, a surgeon is a key member of the treatment team. This surgeon may be a surgical oncologist, a general surgeon, or a colon and rectal surgeon. It is important to have a surgeon who has extensive experience in removing colorectal cancers; this is especially important for people who have rectal cancers because surgical removal of these cancers can be very complex and may involve other pelvic organs or the anal sphincter muscles (the muscles that control bowel movements).

A medical oncologist is also a valuable treatment team member and frequently is the one to coordinate care. Medical oncologists have expertise in treating cancer with drugs and will monitor your health during follow-up and evaluate you carefully for signs of recurrence. A radiation oncologist may also be involved in your care, especially if you have rectal cancer. Several online resources are available to help you find any of these specialists, as well as the best treatment centers (Table 1).

Other health care professionals who may be involved in your care are an oncology nurse, a social worker, a dietician, an ostomy nurse and your primary care physician. As the person with colon or rectal cancer, you are the most important member of the treatment team. Do not be afraid to ask questions about treatment options, to participate in treatment decision-making and to tell your doctors what quality-of-life issues are most important to you.

Learn all you can about your cancer and your treatment options. Knowledge is power.

Table 1. Resources for Finding Specialists in Colon and Rectal Cancers and Cancer Treatment Centers

American Cancer Society:; 800-227-2345;
Finding Treatment Centers: National Cancer Institute Cancer Center Programs
American College of Surgeons:; 312-202-5085;
Cancer Program Accreditation
American Society of Clinical Oncology:;
Find a Cancer Doctor
American Society of Colon and Rectal Surgeons:;
Locate a Colorectal Surgeon
Association of American Cancer Institutes:;
Membership Directory
National Cancer Institute:; 800-422-6237;
How to Find a Doctor or Treatment Facility if You Have Cancer
National Comprehensive Cancer Network:;
Find a NCCN Member Institution
Society of Surgical Oncology:;
Find a Surgical Oncologist

Additional Sources of Information



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