Cancers that are originated from colon or rectum are called colorectal cancer although these cancers can be directly named as colon cancer or rectum cancer depending on the region they are originated from, they are considered within a common group due to many properties they share.

Cancer develops as a result of uncontrolled cell growth within the body. Cells in almost every part of our bodies can become cancerous and spread to other regions.


How Does Colorectal Cancer Start?

Majority of the colorectal cancers start with growths called polyps within the inner layer of the colon or rectum. It takes years for some polyp types to turn into cancer, and not all polyps become cancerous. The risk of becoming cancerous is directly related to the type of a polyp. There are 2 main polyp types:

 Adenomatous polyps (adenomas): As these polyps can turn into cancer, they are considered pre-cancerous lesions.

 Hyperplastic and inflammatory polyps: These polyps are more frequent and they generally do not become cancerous.

Dysplasia; This is another pre-cancerous formation. In this case, some cells in the inner layers of the colon or rectum or in a part of a polyp have lost their normal structure but they are not like real cancer cells yet.

Colon and rectum walls have consisted of many layers. Colorectal cancer develops in the innermost layer called mucosa and starts to grow into the other layers when cancer cells are in the intestinal wall, they may grow into the small blood vessels or lymph canal located there and they may spread to surrounding lymph nodes or other distant parts of the body.


Cancer Types in Colorectal Cancer

Adenocancers constitute 95% of the colon and rectum cancers. These cancers develop in the cells of glands that secrete mucus, which enables lubricity in the colon and rectum. Colorectal cancer almost always means this type of cancer however there are rare colon and rectum cancer types as well. These are;

 Carcinoid Tumors: They develop in some specialized hormone-secreting cells in the intestines.

 Gastrointestinal Stromal Tumor (GIST): These tumors develop from some special cells called Cajal cells that are located in the colon wall and they may not always be malign (cancerous) although these tumors may be present anywhere within the digestive system, they are rarely found in the colon.

 Lymphoma: Typically, they are immune system cancers that originate from lymph nodes, however, they may also emerge directly in the colon, rectum, or other organs.

 Sarcoma: They can originate from blood vessels, muscle layers, or other connective tissues located in the colon or rectum walls. Colorectal sarcomas are very rare.