MedifocusHealth

The colon and the rectum are parts of the digestive system. They form a long, muscular tube called the large intestine ("large bowel"). The colon is the first 4 to 5 feet of the large intestine, and the rectum is the last several inches. Partly digested food enters the colon from the small intestine. The colon removes water and nutrients from the food and turns the rest into waste (stool). The waste passes from the colon into the rectum and then out of the body through the anus.

Cancer of the colon or rectum is called colorectal cancer. In the United States, it is the fourth most common cancer in men and women. The lifetime risk of developing colorectal cancer is 6% for both men and women.

Caught early, colorectal is often curable. In fact, it has been recognized that almost all colorectal cancers arise from benign precursor lesions in the colon (adenomatous polyps), making screening for colorectal cancer a critical issue for this disease. It has been shown that the progression to malignancy (carcinogenesis) occurs in a stepwise fashion, characterized by changes in specific genes. The time required for carcinogenesis ("dwell time") has been estimated to be as long as 10 years, however, some studies have suggested a range of 3 to 14 years. People with a history of adenomatous polyps (benign growths of the colon or rectum) are at increased risk of developing cancer, and removal of adenomas lessens the subsequent incidence of colorectal cancer. Most adenomatous polyps, however, do not progress to cancer particularly if they are very small (less than 1 cm).

Once adenomatous polyps have been removed the rate of recurrence is between 35-50% within 3 years so follow up screening remains important. The risk for recurrence is increased if:

• There are 3 or more adenomas present at time of initial finding
• The patient is age > 60 years
• There is a family history of colorectal cancer

In rare cases, people with another type of cancer may also develop colorectal cancer. Examples include:

• Lymphoma
• Carcinoid tumors
• Melanoma
• Sarcomas

Sometimes, colorectal cancers present with more than one tumor ("synchronous") or can occur at different times ("metachronous"). In fact, 2-7% of persons with colorectal cancer have 1 or more synchronous tumors in the colon and rectum at the time of initial diagnosis. When colorectal cancer spreads (metastasizes), the liver is the most common site of metastatic disease.

Despite advances in managing this disease, the 5 year survival rate in the United States is only 62%, because only 38% of persons with colorectal cancer are diagnosed when the cancer is limited to the bowel wall. Thus, screening for the disease is very important to allow early detection and treatment.

Most colon cancers are adenocarcinomas. Mucinous carcinomas are tumors that are comprised of 30-60% mucus. They account for 10-15% of all adenocarcinomas. It is thought that the presence of mucus allows malignant cells to spread faster. Mucinous carcinomas are considered more aggressive than regular carcinomas and are more difficult to treat.