Colorectal cancers are thought to develop slowly over a period of several years. Before a true cancer develops, there usually are precancerous changes in the lining of the colon or rectum. These changes might be dysplasia (abnormal cells) or adenomatous polyps. A polyp is a growth of tissue into the center of the colon or rectum.

More than 95 percent of colorectal cancers are adenocarcinomas. These are cancers of the glandular cells that line the inside of the colon and rectum. Other less common types of tumors found in the colon and rectum include:

• Carcinoid tumors: tumors of hormone-producing cells of the intestine,
• Gastrointestinal stromal tumors: tumors of the connective tissue in the wall of the colon and rectum, and
• Lymphomas: cancers of the immune cells in the colon and rectum, lymph nodes, and other organs.

About 94,700 new cases of colon cancer (43,000 men and 51,700 women) and 34,700 new cases of rectal cancer (19,400 men and 15,300 women) are expected to be diagnosed in 1999 in the US. Colon cancer is expected to cause about 47,900 deaths (23,000 men and 24,900 women) this year, and about 8,700 people (4,800 men and 3,900 women) will die from rectal cancer.

The number of people dying from colorectal cancer has been going down for the past 20 years. This may be because there are fewer cases, more cases are found early, and treatment has improved.

The five-year survival rate is 92 percent for people whose colorectal cancer is found and treated in an early stage, before it has spread. But, only 37 percent of colorectal cancers are found at that early stage. Once the cancer has spread to nearby organs or lymph nodes, the five-year survival rate drops to 64 percent. For people whose colorectal cancer has spread to distant parts of the body such as the liver or lungs, the five-year survival rate is seven percent.

Risk factors for colorectal cancer include:

• A family history of colorectal cancer: If a family member has had colorectal cancer, talk with your doctor about your individual risk and when screening tests should begin.
• A personal history of colorectal cancer: Even when a colorectal cancer has been completely removed, new cancers may develop in other areas of the colon and rectum.
• A personal history of intestinal polyps: Some types of polyps do not increase the risk of colorectal cancer, but other types, such as adenomatous polyps, do increase the risk of colorectal cancer, especially if they are large or numerous.
• A personal history of chronic inflammatory bowel disease: Chronic inflammatory bowel disease (ulcerative colitis or Crohn’s disease) is a condition in which the colon is inflamed over a long period of time and may have ulcers in its lining.
• Aging: About 90 percent of people found to have colorectal cancer are older than 50.

The three main types of treatment for colon cancer are surgery, radiation therapy, and chemotherapy. Depending on the stage of the cancer, two or even three of these types of treatment may be combined at the same time or one after another.