Colorectal Cancer

Colon cancer begins in the colon; rectal cancer begins in the rectum. Colorectal cancer is a more general term that encompasses cancers that begin in either the colon or the rectum. Although colon and rectal cancers are similar, there are some differences in how they develop and are treated. Each year about 130,000 people are diagnosed with colorectal cancer. Most of the people who develop colorectal cancer are over 50. Women are more likely to develop cancer of the colon, and men are more likely to develop cancer of the rectum.

In addition to age, the following are risk factors for colorectal cancer: a history of polyps (growths that protrude into the colon or rectum), a family history of colorectal cancer, a history of ulcerative colitis or Crohn's disease, and a diet high in fat and low in fiber. To help prevent colorectal cancer, people should eat a diet low in fat and high in fiber, avoid drinking excessive amounts of alcohol, maintain a healthy weight through diet and exercise, and take an aspirin daily. Many colon cancers start in polyps, so doctors help prevent colorectal cancer by removing polyps when they find them.

Symptoms

In early colorectal cancer, a person may be free of any symptoms or have slight bleeding in the stool. Other symptoms include:

• A change in bowel habits, such as prolonged constipation or diarrhea or bowel (fecal) incontinence (the unintentional release of stool)
• Blood in the stool
• Unusual stomach or gas pains
• Unexplained weight loss
• Fatigue
• Vomiting

Having these symptoms does not necessarily mean that a person has colorectal cancer. However, because colorectal cancer that is detected early can be cured, a doctor should be consulted if any of these symptoms occur.

Screening and Diagnosis

Many experts recommend regular screening for colorectal cancer beginning at age 50. Several screening methods are available. One approach is to undergo a digital rectal examination (in which a doctor inserts a gloved finger into the rectum and feels for any abnormalities) and a test to detect hidden blood in the stool (fecal occult blood testing) every year. Some experts also suggest that the colon and rectum be examined with sigmoidoscopy, or preferably with colonoscopy, at age 50. Sigmoidoscopy allows the doctor to examine the lower portion of the colon; colonoscopy allows examination of the entire colon. Any polyps found are removed, and the examination is repeated in a year. If no polyps are found, testing can be repeated in 5 to 10 years.

Virtual colonoscopy is a term being used to describe screening that uses computed tomography (CT) scanning without actual sigmoidoscopy or colonoscopy. Many people avoid colonoscopy because the test is cumbersome to prepare for or because they fear the examination itself. Although a virtual colonoscopy is less intrusive, the colon must still be cleansed the same as for colonoscopy with a flexible viewing tube called a colonoscope. And if abnormalities are detected with virtual colonoscopy, colonoscopy must then be performed so that a biopsy can be done.

See the figure Staging Colon Cancer.

If an abnormality is detected with a screening test, the doctor removes tissue for examination under a microscope (biopsy). If the abnormality is a polyp, the entire polyp is removed. Once a cancer is diagnosed, further examinations are done to see whether the cancer has spread (staging).

Treatment

Treatment depends on how far the cancer has spread. Usually, the first step is surgery to remove the cancer and the area around it.

The type of surgery depends on the area where the cancer is and how far it has spread. Partial colectomy involves removing the part of the colon where cancer is located and then attaching the ends of the remaining colon to each other. Usually, bowel habits return to normal or almost normal after this type of surgery.

If the cancer is more extensive, larger parts of the colon and rectum may need to be removed. Doctors have to create an opening in the skin of the abdomen so that stool can be eliminated from the body. This opening is called a stoma or an ostomy. Because the colon is involved, the opening is called a colostomy. A colostomy may be temporary (until the surgical site has healed) or permanent.

See the figure Understanding Colostomy.

If the cancer has spread outside the colon or rectum, chemotherapy, radiation therapy, or both may be used to ensure that cancer cells are killed. Chemotherapy with fluorouracil may prolong survival if colon cancer has spread to nearby lymph nodes. If colon cancer has spread more widely, to organs such as the liver, chemotherapy with fluorouracil or irinotecan does not improve survival but it may help improve symptoms. However, chemotherapy can cause many side effects. Radiation therapy may help reduce pain in some people with colon cancer that has spread widely. Chemotherapy and radiation therapy may help prolong survival in some people with rectal cancer that has spread beyond the rectum, but both may cause many side effects.

Outlook

The outlook after surgery for colorectal cancer very much depends on the stage of the cancer at diagnosis. However, it also depends on how well the person responds to treatment and the person's general health. More than 90% of people with colorectal cancer that is limited to the inner lining of the colon or rectum or that has grown no further than the layer of tissue just under the inner lining will live at least 5 years after treatment. However, if the cancer extends into nearby lymph nodes or has spread to other organs, the likelihood of living at least 5 years after treatment is greatly decreased.

Even after successful treatment, colorectal cancer recurs in about one third of people within 3 to 5 years. Chemotherapy and radiation therapy after surgery have reduced the likelihood of recurrence for many people, but both can cause many side effects. Regular examinations by a doctor are important. Doctors recommend that most people undergo blood tests to look for carcinoembryonic antigen (CEA), an indicator of some kinds of cancer cells, every 2 to 3 months for 2 to 5 years after treatment.

Colonoscopy should be performed every 2 to 3 years to look for evidence that the cancer has recurred and for new tumors or polyps.