Colon and Rectal Cancer

What Is Colorectal Cancer?

Colorectal cancer is a term used to refer to cancer that develops in the colon or the rectum. These cancers are sometimes referred to separately as colon cancer or rectal cancer, depending on where they start.

In most people, colorectal cancers develop slowly over a period of several years. Before a cancer develops, a growth of tissue or tumor usually begins as a non-cancerous polyp on the inner lining of the colon or rectum. A tumor is abnormal tissue and can be benign (not cancer) or malignant (cancer).

A polyp is a benign, non-cancerous tumor.  Some polyps can change into cancer, but not all do.  Several types of polyps can become cancerous.  Large polyps are more likely to become cancerous than small ones.  Removing a polyp early may prevent it from becoming cancer.

The chance of a polyp changing into a cancer depends upon the kind of polyp:

Adenomas, adenovillous and villous adenomas are polyps that have the potential to change into cancer.  Because of this, they are called a pre-cancerous condition.

Hyperplastic polyps and inflammatory polyps, in general, are not pre-cancerous.  But some doctors think that some hyperplastic polyps can become pre-cancerous or might be a sign of having a greater risk of developing adenomas and cancer.

More than 95% of colorectal cancers are a type of cancer known as adenocarcinomas. These are cancers that start in cells that are glands inside of the colon and rectum.  When doctors speak of colorectal cancer, this is almost always what they are referring to.

In later stages of the disease, cancerous tumors may penetrate the colon wall.  These tumors may also spread (metastasize) to nearby lymph nodes or other organs.