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How Colon Cancer Develops

April 15, 2024

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Even if you understand the importance of getting a colonoscopy to screen for colorectal cancer, you might not know how cancer develops in this crucial organ.

The colon and rectum have an inner lining called the mucosa or epithelium, which contains epithelial cells. The mucosa helps the colon form and move feces, as well as maintain a proper balance of electrolytes and water, explains Ira Leeds, MD, a Yale Medicine colorectal surgeon.

“The mucosa works overtime to keep the process going in a smooth and predictable fashion, and to do so, just like the skin on the outside of your body, it's turning over all the time,” Dr. Leeds says.

But, sometimes, mistakes occur in that cell turnover process. “And for the colon, because it's happening at such a high frequency, those errors come up more frequently than they would in your eye or heart,” Dr. Leeds adds.

In the colon and rectum, those abnormal clusters of cells are called polyps, or growths from the lining of the colon that project into the lumen of the bowels. As more errors develop in the cells that form the lining, a polyp can turn into cancer.

“One of the main parts of my job is to encourage people to be screened for colorectal cancer. Through screening, we're able to identify polyps at very early stages,” says Taneisha Grant, MD, a Yale Medicine gastroenterologist.

The gold standard screening is a colonoscopy, during which the doctor uses a thin, flexible tube with a camera at the end to examine the colon and the rectum.

“During a colonoscopy, we are looking carefully at the walls and lining of the colon. We take biopsies, or small tissue samples, and we’re also able to remove the polyps completely during the procedure,” Dr. Grant says.

Removing polyps reduces their risk of developing into cancer.

It’s important to note, Dr. Grant says, that routine colonoscopies for someone at average risk of colorectal cancer are now recommended to start at age 45. The recommendation used to be age 50, but it has been lowered due to a rise in growing rates of colorectal cancer in younger people.

Yale Medicine physicians talk more about colorectal cancer and screening in the video above.