Colorectal cancer is second leading cause of cancer deaths among American men and women. These cancers arise from the lining of the large intestine, also known as the colon. Tumors may also arise from the lining of the very last part of the colon, called the rectum.

Unfortunately, most colorectal cancers are "silent" tumors. They grow slowly and often do not produce symptoms until they reach a large size. Fortunately, colorectal cancer is preventable, and curable, if detected early.

How Does Colorectal Cancer Develop?

Colorectal cancer usually begins as a polyp. The word "polyp" is a nonspecific term to describe a bump on the surface of the colon. Polyps can also be bumps of normal colorectal lining which do not increase the risk of colorectal cancer.

The two most common types of polyps found in the large intestine include:

Hyperplastic polyps. Usually small, left-sided polyps that do not carry a risk of developing into cancer. However, large hyperplastic polyps, especially on the right side of the colon, are of concern and should be completely removed.
Adenomas or adenomatous polyps. Benign polyps, which, if left alone, could turn into colon cancer.

Although most colorectal polyps never become cancer, virtually all colon and rectal cancers start from these benign growths.

Polyps and colon cancer develop when there are mutations or errors in the genetic code that controls the growth and repair of the cells lining the colon. People may inherit diseases in which the risk of colon polyps and cancer is very high.

What Are the Risk Factors for Colorectal Cancer?

While anyone can get colorectal cancer, it is most common among people over the age of 50. Risk factors for colorectal cancer include:

A personal or family history of colorectal cancer or polyps.
A diet high in fat and low in fiber.
Inflammatory bowel disease (Crohn's disease or ulcerative colitis).
Obesity.
Smoking.

What Are the Symptoms of Colorectal Cancer?

Unfortunately, colorectal cancer may strike without symptoms. For this reason, it is very important to be screened regularly by your doctor for colorectal cancer, even if you have no symptoms.

There are a number of tests your doctor can perform to diagnose colorectal cancer. These tests include:

Sigmoidoscopy. This is a procedure used to examine the very last part of the colon (sigmoid colon and rectum). This test can detect polyps, tumors, and other changes in the sigmoid colon and rectum. During this exam, a biopsy (tissue sample) can also be taken for testing.
Colonoscopy. A colonoscopy examines the entire colon and rectum. During this procedure, a biopsy may be taken.
Colon X-rays. Also known as a barium enema or lower GI, this test provides an outline of the colon lining as well as detects polyps, tumors, and changes in the colon and rectum.
Colonography. This is an X-ray done of the entire colon using a CT (computed tomography) scanner. This test takes less time and is less invasive than a colonoscopy. It also does not require anesthesia. It can detect polyps usually greater than 1cm. However, if a polyp is detected, a standard colonoscopy needs to be performed. Use of this study remains controversial because it may miss up to 10% of polyps that are present.