Colorectal cancer starts in the colon or the rectum. These cancers can also be referred to separately as colon cancer or rectal cancer, depending on where they start, though they have many aspects in common.
This type of cancer usually develops slowly over the course of a number of years, often beginning as a non-cancerous polyp on the inner lining of your colon or rectum. Polyps are usually benign, or not cancerous. If not removed, they can evolve into cancer but don’t always. It depends on the type of polyp.
- Adenomatous polyps (adenomas) are polyps that can change into cancer, and are referred to as pre-cancerous.
- Hyperplastic polyps and inflammatory polyps are usually not pre-cancerous.
Another kind of pre-cancerous condition is called dysplasia. Dysplasia is an area in the lining of the colon or rectum where the cells look abnormal (but not like true cancer cells) when viewed under a microscope. These cells can change into cancer over time. Dysplasia can also be seen in people who have had diseases such as ulcerative colitis or Crohn's disease for many years. Both ulcerative colitis and Crohn's disease cause chronic inflammation of the colon.
The colon is a muscular tube about five to six feet long that is part of the large intestine. The rectum is the lower six inches of the large intestine. The colon absorbs water and nutrients from food, and the rectum serves as the holding place for the stool.
The colon is divided into four sections: the ascending colon, transverse colon, descending colon, and sigmoid colon. Most colorectal cancers arise in the sigmoid colon — the portion just above the rectum. They usually start in the innermost layer and can grow through some or all of the several layers of tissue that make up the colon and rectum. The extent to which a cancer penetrates the various tissue layers determines the stage of the disease.
A small percentage of colorectal cancers — usually hereditary forms of the disease — can cause large numbers of polyps to appear, but these types of colorectal cancers are rare.
Colorectal cancers are usually contained within the colon, but when they become advanced the cancer can metastasize, or spread, to other organs. When colorectal cancer spreads, it tends to move to the liver and lungs.
At Providence Saint John’s, we treat your cancer with a team of highly-skilled physicians and nurses who focus on delivering the most advanced care to help increase your chances of living a healthy life. We do that with leading-edge treatments for colorectal cancer that include minimally-invasive laparoscopic and robotic surgical procedures.