Colon and Rectum Cancer: What You Need To Know

by National Cancer Institute

Cancer of the colon or rectum is also called colorectal cancer. In the United States, colorectal cancer is the fourth most common cancer in men, after skin, prostate, and lung cancer. It is also the fourth most common cancer in women, after skin, lung, and breast cancer.

The Colon and Rectum

The colon and rectum are parts of the digestive system. They form a long, muscular tube called the large intestine (also called the large bowel). The colon is the first 4 to 5 feet of the large intestine, and the rectum is the last 4 to 5 inches. The part of the colon that joins to the rectum is the sigmoid colon. The part that joins to the small intestine is the cecum.

Partly digested food enters the colon from the small intestine. The colon removes water and nutrients from the food and stores the rest as waste. The waste passes from the colon into the rectum and then out of the body through the anus.

Understanding Cancer

Cancer begins in cells, the building blocks that make up tissues. Tissues make up the organs of the body.

Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die, and new cells take their place.

Sometimes this orderly process goes wrong. New cells form when the body does not need them, and cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor.

Tumors can be benign or malignant:

Benign tumors are not cancer:

• Benign tumors are rarely life-threatening.
• Generally, benign tumors can be removed, and they usually do not grow back.
• Cells from benign tumors do not invade the tissues around them.
• Cells from benign tumors do not spread to other parts of the body.

Malignant tumors are cancer:

• Malignant tumors are generally more serious than benign tumors. They may be life-threatening.
• Malignant tumors usually can be removed, but sometimes they grow back.
• Cells from malignant tumors can invade and damage nearby tissues and organs.
• Cells from malignant tumors can spread to other parts of the body. The cells spread by breaking away from the original cancer (primary tumor) and entering the bloodstream or lymphatic system. They invade other organs, forming new tumors and damaging these organs. The spread of cancer is called metastasis.

Colorectal Cancer

Cancer that begins in the colon is called colon cancer, and cancer that begins in the rectum is called rectal cancer. Cancers affecting either of these organs may also be called colorectal cancer.

When colorectal cancer spreads outside the colon or rectum, cancer cells are often found in nearby lymph nodes. If cancer cells have reached these nodes, they may also have spread to other lymph nodes, the liver, or other organs.

When cancer spreads (metastasizes) from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if colorectal cancer spreads to the liver, the cancer cells in the liver are actually colorectal cancer cells. The disease is metastatic colorectal cancer, not liver cancer. It is treated as colorectal cancer, not liver cancer. Doctors sometimes call the new tumor "distant" or metastatic disease.

Colorectal Cancer: Who's at Risk?

No one knows the exact causes of colorectal cancer. Doctors can seldom explain why one person develops the disease and another does not. However, it is clear that colorectal cancer is not contagious. No one can "catch" this disease from another person.

Research has shown that people with certain risk factors are more likely than others to develop colorectal cancer. A risk factor is anything that is linked to an increased chance of developing a disease.

Studies have found the following risk factors for colorectal cancer:

Age: Colorectal cancer is more likely to occur as people get older. More than 90 percent of people with this disease are diagnosed after age 50. The average age at diagnosis is in the mid-60s.

Colorectal polyps: Polyps are growths on the inner wall of the colon or rectum. They are common in people over age 50. Most polyps are benign (noncancerous), but some polyps (adenomas) can become cancer. Finding and removing polyps may reduce the risk of colorectal cancer.

Family history of colorectal cancer: Close relatives (parents, brothers, sisters, or children) of a person with a history of colorectal cancer are somewhat more likely to develop this disease themselves, especially if the relative had the cancer at a young age. If many close relatives have a history of colorectal cancer, the risk is even greater.

Genetic alterations: Changes in certain genes increase the risk of colorectal cancer.

Hereditary nonpolyposis colon cancer (HNPCC) is the most common type of inherited (genetic) colorectal cancer. It accounts for about 2 percent of all colorectal cancer cases. It is caused by changes in an HNPCC gene. About 3 out of 4 people with an altered HNPCC gene develop colon cancer, and the average age at diagnosis of colon cancer is 44.

Familial adenomatous polyposis (FAP) is a rare, inherited condition in which hundreds of polyps form in the colon and rectum. It is caused by a change in a specific gene called APC. Unless familial adenomatous polyposis is treated, it usually leads to colorectal cancer by age 40. FAP accounts for less than 1 percent of all colorectal cancer cases.

Family members of people who have HNPCC or FAP can have genetic testing to check for specific genetic changes. For those who have changes in their genes, health care providers may suggest ways to try to reduce the risk of colorectal cancer, or to improve the detection of this disease. For adults with FAP, the doctor may recommend an operation to remove all or part of the colon and rectum.

Personal history of colorectal cancer: A person who has already had colorectal cancer may develop colorectal cancer a second time. Also, women with a history of cancer of the ovary, uterus (endometrium), or breast are at a somewhat higher risk of developing colorectal cancer.

Ulcerative colitis or Crohn's disease: A person who has had a condition that causes inflammation of the colon (such as ulcerative colitis or Crohn's disease) for many years is at increased risk of developing colorectal cancer.

Diet: Studies suggest that diets high in fat (especially animal fat) and low in calcium, folate, and fiber may increase the risk of colorectal cancer. Also, some studies suggest that people who eat a diet very low in fruits and vegetables may have a higher risk of colorectal cancer. More research is needed to better understand how diet affects the risk of colorectal cancer.

Cigarette smoking: A person who smokes cigarettes may be at increased risk of developing polyps and colorectal cancer.

People who think they may be at risk should discuss this concern with their doctor. The doctor may be able to suggest ways to reduce the risk and can plan an appropriate schedule for checkups.

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