Colorectal cancer is the second most preventable cancer, after lung cancer. When the cancer is found early, initial treatment can often lead to an excellent outcome. Colorectal cancer is cancer that occurs in the large intestine and rectum. The colon is a muscular tube that is about five feet long. It absorbs water and nutrients from food. The rectum, the lower six inches of the digestive tract, serves as a holding place for stool, which then passes out of the body through the anus. Although many people think of colorectal cancer as a disease that primarily affects men, it is slightly more common in women. Today, the average person has about a 1 in 20 chance of developing colorectal cancer during his or her life.

The colon is divided into four sections: the ascending colon, transverse colon, descending colon, and sigmoid colon. Most colorectal cancers arise in the sigmoid colon -- the portion just above the rectum. They usually start in the innermost layer and can grow through some or all of the several tissue layers that make up the colon and rectum. The extent to which a cancer penetrates the various tissue layers determines the stage of the disease. Most colorectal cancers grow slowly over a period of several years, often beginning as small benign growths called polyps. Removing these polyps early, before they become malignant, is an effective means of preventing colorectal cancer.

Colorectal cancer sometimes arises without any symptoms. For this reason, screening tests (such as colonoscopy and a test for blood in the stool) are recommended to detect the cancer early, when it is more curable.

When symptoms do occur, however, they may include the following:

• Rectal bleeding or blood in the stool
• A change in bowel habits (such as diarrhea, constipation, and narrowing of the stool) that lasts for more than a few days
• Abdominal pain
• A continuous feeling that you need to have a bowel movement, which does not resolve after passing stool
• Weakness

Some of these symptoms may be caused by other conditions. But you should see your doctor if they persist. Any incidence of rectal bleeding or blood in the stool should be brought to your doctor's attention.

The best way to cure colorectal cancer is to prevent it from occurring in the first place. A regular program of screening examinations is the best way to ensure an early diagnosis, and an early diagnosis offers the best chance for a cure

Colorectal cancer screening and diagnosis may involve one or more of a number of procedures:

This examination allows the doctor to inspect the rectum and colon, using a thin tube that has a light on the end. It is inserted into the rectum while the patient lies on his or her side. Patients often receive a mild sedative during this procedure to ensure their comfort. Any polyps or other growths that are found during these examinations are usually removed at the time and sent to a laboratory for examination.

A ten-year study by Tata Memorial Centre investigators showed that colonoscopy was more effective than another screening technique called double-contrast barium enema for detecting precancerous colon polyps. The findings of this study were the first to show that the various surveillance tools used to follow patients who have had colon polyps removed are not equally reliable. Moreover, unlike barium enema, colonoscopy allows the doctor to remove any polyps at the time of the examination.

Also known as a stool blood test, this laboratory test looks for blood in the stool. The patient is asked to follow a special diet and then bring in stool specimens (usually applied to small, folded cards) from three successive days.

This examination is similar to the colonoscopy exam, but it uses a shorter tube to inspect the lower colon.

Virtual colonoscopy is a new technique that uses CT scans to create a 3-D image that can be used to evaluate the bowel. At this time, it is still a research tool and is not generally available. It is also important to note that, while this is a promising technique, it does not allow for a biopsy or polyp removal at the same time an abnormality is found.

The choice of treatment for colorectal cancer depends on the stage of the disease -- that is, how large the tumor has grown, how deeply it has invaded the layers of the colon or rectum, and whether it has spread to other organs (most commonly the liver), lymph nodes, or other parts of the body.

Treatment options include surgery, radiation therapy, chemotherapy, and combinations of these approaches.