The colon is the part of the digestive system where the waste material is stored. The rectum is the end of the colon adjacent to the anus. Together, they form a long, muscular tube called the large intestine (also known as the large bowel). Tumors of the colon and rectum are growths arising from the inner wall of the large intestine. Benign tumors of the large intestine are called polyps. Malignant tumors of the large intestine are called cancers.

Colon cancer is cancer of the large intestine (colon), the lower part of your digestive system. Rectal cancer is cancer of the last 6 inches of the colon. Together, they're often referred to as colorectal cancers. About 112,000 people are diagnosed with colon cancer annually, and about 41,000 new cases of rectal cancer are diagnosed each year, according to the American Cancer Society.

Most colorectal cancers begin as a polyp (say "pahl-ip"). At first, a polyp is a small, harmless growth in the wall of the colon. However, as a polyp gets larger, it can develop into a cancer that grows and spreads.

Common Causes of Colon Cancer

Most colorectal cancers arise from adenomatous polyps-clusters of abnormal cells in the glands covering the inner wall of the colon. Over time, these abnormal growths enlarge and ultimately degenerate to become adenocarcinomas.

Adenomas: These polyps have the potential to become cancerous and are usually removed during screening tests such as flexible sigmoidoscopy or colonoscopy.

Alcohol: Research has indicated that alcohol increases colorectal cancer risk. Research has also shown that it lowers it, or that it has no effect at all. So which is right? All of it may be. The key appears to be what kind of alcohol you're drinking.

Inflammatory polyps: These polyps may follow a bout of ulcerative colitis. Some inflammatory polyps may become cancerous, so having ulcerative colitis increases your overall risk of colon cancer.

Age: About 90 percent of people diagnosed with colon cancer are older than 50. Colon cancer can occur in younger people, but it occurs much less frequently.

Environment: Research has shown that environment can play a big part in colon cancer development. Where you live, who's around you, your occupation, and even when you work may all influence your risk of developing colon cancer.

Diets high in fat are believed to predispose humans to colorectal cancer. In countries with high colorectal cancer rates, the fat intake by the population is much higher than in countries with low cancer rates. It is believed that the breakdown products of fat metabolism lead to the formation of cancer-causing chemicals (carcinogens). Diets high in vegetables and high-fiber foods such as whole-grain breads and cereals may rid the bowel of these carcinogens and help reduce the risk of cancer.

Hereditary nonpolyposis colon cancer (HNPCC) syndrome is a genetic condition characterized by early-onset colorectal cancer (i.e., develops before age 50) and multiple colorectal cancers. This syndrome also may be associated with other cancers (e.g., cancer of the small intestine, endometrium, stomach, and renal pelvis).

Smoking: Smoking may increase the risk of developing colorectal cancer by as much as 40%. Smokers may swallow some of the cancer-causing chemicals and this may be an explanation for the increased risk of colorectal cancer in smokers. Some of these substances are also absorbed into the bloodstream thus causing increased risk of many cancers.