Colorectal cancer is a type of cancer that affects the colon (the longest part of the large intestine) and the rectum (the last few inches of the colon connected to the anus). The National Cancer Institute (NCI) reports that colon cancer caused nearly 50,000 deaths in 2009. About 60 percent of deaths from colorectal cancer could have been prevented by regular screening tests, says the U.S. Centers for Disease Control and Prevention. Colorectal cancer is classified by five different developmental stages, which can be identified based upon specific features.
Stage 0
The earliest stage of colorectal cancer is called Stage 0, according to the American Cancer Society (ACS) and the National Cancer Institute (NCI). This is the first stage of colorectal cancer and only affects the mucosa, which is the innermost lining of the colon or rectum. The cancerous cells have not grown beyond this layer.
Stage I
The second stage of colorectal cancer is referred to as Stage I. This stage of cancer is defined as involving the inner muscle layer (also called the muscularis mucosa) and extends into the submucosa; the submucosa is the layer immediately under the inner muscle layer. Colorectal cancer in this stage, however, has not grown through the wall of the colon or rectum.
Stage II
This stage of colorectal cancer, called Stage II by the NCI and ACS, is characterized by tumor(s) that extend into or through the outermost wall of the colon or rectum. It may also invade nearby tissue, but has not spread further into lymph nodes or other distant sites.
Stage III
The fourth stage of colorectal cancer is Stage III, defined by the NCI and the ACS as grown through the wall of the colon or rectum, and spreads to nearby tissues and organs. It has also spread to nearby lymph nodes, but not to other distant sites.
Stage IV
This stage of colorectal cancer means that the cancerous cells have grown through the wall of the colon or rectum, and may have spread to nearby lymph nodes. The feature that distinguishes Stage IV colorectal cancer is that it has spread to organs that may be far way from the colon and rectum. According to NCI and ACS, these organs include liver, lung, ovary, and peritoneum (the lining of the abdominal cavity).
