Cancer happens when cells in your body go through changes that make them grow out of control. Colorectal cancer is cancer that starts in either your colon or your rectum, which together make up the lower part of your digestive tract. It is the third most common cancer for both men and women. Cancer usually does not start in both the colon and rectum. But both types of cancer have a lot in common. So they are often referred to as "colorectal" cancer.
Most cancers in the colon or rectum begin in the inner lining as a polyp. A polyp is an abnormal growth of tissue and can occur in other places besides your colon or rectum, such as inside your nose. Not all polyps become cancers. But over a period of years, some polyps, if they are allowed to grow, do.
When a colon cancer is identified during a routine screening, it is likely that it has been growing for several years. The original cancer is called the primary tumor. Your colon has several layers of tissue, and as the primary tumor grows, it extends through these layers. Once it has grown through all the layers, the cancer can spread to nearby tissue or organs. Frequently, by the time colorectal cancer is found, some of the cells have already spread to other parts of the body, such as lymph nodes, liver or lungs. This process is called metastasis, and it's what makes colorectal cancer especially life-threatening. That doesn't mean you can't beat colorectal cancer. You and your healthcare team have a lot of treatment options to choose from once you all understand the nature of your cancer.
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