Colon cancer is a type of cancer that begins in the large intestine (colon). It is often grouped with rectal cancer because of the many features they have in common. Colon cancer is typically seen in older adults, though it can happen at any age.

How Does Colon Cancer Start?

Most colorectal cancers start as a growth, known as a polyp, on the inner lining of the colon or rectum. There are different types of polyps, and some may change into cancer over time, but not all become cancer. Certain polyps have a higher chance of developing into cancer. Regular colonoscopy screenings are so important because it can detect and remove these polyps before they have the opportunity to grow into cancer. Polyps that can develop in the colon or rectum include:

• Adenomatous polyps (adenomas): These are polyps that have the potential to turn into cancer and are often referred to as pre-cancerous polyps.
• Hyperplastic polyps and inflammatory polyps: These polyps are generally not pre-cancerous. Those with large hyperplastic polyps may be recommended to get a colorectal cancer screening every ten years.
• Sessile serrated polyps and traditional serrated adenomas: These polyps are treated very similarly to adenomas because they have a higher risk of colorectal cancer.

Other factors that contribute to the likelihood of a polyp becoming cancerous include:

• If a polyp larger than 1 centimeter is found
• If more than three polyps are found
• If dysplasia is seen in the polyp after it’s removed. Dysplasia is another pre-cancerous condition. It means there’s an area in a polyp or lining of the colon where the cells look abnormal but haven’t become cancer.

How Does Colon Cancer Spread?

If cancer forms in a polyp, it can grow into the wall of the colon or rectum over time. The wall of the colon is made of many layers. Colorectal cancer starts in the innermost layer and can grow outward through some or all the layers. Once cancer cells are in the wall, they grow into blood vessels or lymph vessels, which are tiny channels that carry away waste and fluid. Once they grow into blood vessels or lymph vessels, they can travel to nearby lymph nodes or distant parts of the body.

The stage or spread of colorectal cancer depends on how deeply it grows into the wall of the colon and if it has spread to other parts of the body. To learn about the symptoms of colon cancer, click here.

Types of Colorectal Cancer

Most colorectal cancers are adenocarcinomas. These cancers start in cells that make mucus to lubricate the inside of the colon and rectum. When doctors talk about colorectal cancer, this is more commonly what they’re referring to. There are sub-types of adenocarcinomas, and some may have a worse prognosis than others.

Other types of tumors may start in the colon and rectum include:

• Carcinoid tumors: These start from special hormone-making cells in the intestine. You may learn more about these tumors by clicking here.
• Lymphomas: These are cancers of immune system cells. They usually start in lymph nodes but can also start in the colon, rectum or other organs.
• Sarcomas: These start in blood vessels, muscle layers and other connective tissues in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare.

The Ochsner Cancer Institute is at the forefront of colon cancer and rectal cancer prevention through patient screening, education, detection and treatment. Ochsner's colorectal surgeons specialize in the surgical removal of malignancies of the colon, rectum and anus. They offer a full range of surgical options and are nationally recognized authorities on anal and perianal tumors.