What is Colorectal Cancer?
Colon Cancer And Rectal Cancer Are Often Grouped Together Because They Have Many Features In Common
Colorectal cancer is the third most common cancer diagnosed in both men and women in the United States. It is the third leading cause of cancer-related deaths in the U.S. when men and women are considered separately, and the second leading cause when both sexes are combined.
Colorectal cancer starts in the colon or the rectum. These cancers can also be named colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common.
Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body.
HOW DOES COLORECTAL CANCER START?
Most colorectal cancers begin as a growth on the inner lining of the colon or rectum called a polyp. Some types of polyps can change into cancer over the course of several years, but not all polyps become cancer. The chance of changing into a cancer depends on the kind of polyp. The two main types of polyps are:
- Adenomatous polyps (adenomas): These polyps sometimes change into cancer. Because of this, adenomas are called a pre-cancerous condition.
- Hyperplastic polyps and inflammatory polyps: These polyps are more common, but in general they are not pre-cancerous.
Dysplasia, another pre-cancerous condition, is an area in a polyp or in the lining of the colon or rectum where the cells look abnormal (but not like true cancer cells).
If cancer forms in a polyp, it can eventually begin to grow into the wall of the colon or rectum.
The wall of the colon and rectum is made up of several layers. Colorectal cancer starts in the innermost layer (the mucosa) and can grow through some or all of the other layers. When cancer cells are in the wall, they can then grow into blood vessels or lymph vessels (tiny channels that carry away waste and fluid). From there, they can travel to nearby lymph nodes or to distant parts of the body.
The stage (extent of spread) of a colorectal cancer depends on how deeply it grows into the wall and if it has spread outside the colon or rectum.
THE NORMAL COLON AND RECTUM
The colon and rectum are parts of the digestive system, which is also called the gastrointestinal (GI) system. The colon and rectum make up the large intestine (or large bowel). Most of the large intestine is made up of the colon, a muscular tube about 5 feet long. The colon absorbs water and salt from the remaining food matter after it goes through the small intestine (small bowel).
The waste matter that is left after going through the colon goes into the rectum, the final 6 inches of the digestive system, where it is stored until it passes out of the body through the anus.
TYPES OF CANCER IN THE COLON AND RECTUM
Adenocarcinomas make up more than 95 percent of colorectal cancers. These cancers start in cells that form glands that make mucus to lubricate the inside of the colon and rectum. When doctors talk about colorectal cancer, they are almost always talking about this type.
Other, less common types of tumors can also start in the colon and rectum. These include:
Carcinoid tumors start from specialized hormone-making cells in the intestine.
Gastrointestinal stromal tumors (GISTs) start from specialized cells in the wall of the colon called the interstitial cells of Cajal. Some are non-cancerous (benign). These tumors can be found anywhere in the digestive tract, but it is unusual to find them in the colon.
Lymphomas are cancers of immune system cells that typically start in lymph nodes, but they can also start in the colon, rectum, or other organs.
Sarcomas can start in blood vessels, muscle layers, or other connective tissues in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare.
THE IMPORTANCE OF EARLY DETECTION
Screening is the process of looking for cancer or pre-cancer in people who have no symptoms of the disease. Regular screening can often find colorectal cancer early, when it is most likely to be curable.
In many people, screening can also prevent colorectal cancer by finding and removing polyps before they have the chance to turn into cancer.
COLORECTAL CANCER SCREENING TESTS
Tests used to screen for colorectal cancer include:
- Guaiac-based fecal occult blood test (gFOBT) and fecal immunochemical test (FIT): Samples of stool (feces) are checked for blood, which might be a sign of a polyp or cancer.
- Stool DNA test: A sample of stool is checked for certain abnormal sections of DNA (genetic material) from cancer or polyp cells.
- Sigmoidoscopy: A flexible, lighted tube is inserted into the rectum and lower colon to check for polyps and cancer.
- Colonoscopy: A longer, flexible tube is used to look at the entire colon and rectum.
- Double-contrast barium enema: This is an x-ray test of the colon and rectum.
- CT colonography (virtual colonoscopy): This is a type of CT scan of the colon and rectum.
The gFOBT, FIT, and stool DNA testing mainly find cancer, but can find some polyps.
Sigmoidoscopy, colonoscopy, double contrast barium enema, and CT colonography are good at finding both cancer and polyps. These tests are preferred if they are available and you are willing to have them.
For most adults, the American Cancer Society recommends starting screening with one of these tests at age 50. Some people at higher risk for colorectal cancer might need to start screening earlier.
For more information,visit cancer.org or call the National Cancer Information Center toll-free number, 1-800-227-2345.
Courtesy of the American Cancer Society