The colon and the rectum are components of the gastrointestinal (GI) system or digestive system whose function is to process and convert food into energy, and to purge waste from the body. Colon cancer and rectal cancer have similar characteristics, and are often referred to collectively as "colorectal cancer."
Nearly 73% of new CRC cases occur as colon cancer, while 27% are attributed to rectal cancer.
The walls of the colon and rectum are comprised of layers of tissue. CRC often begins as an intestinal polyp on the innermost layer, and from there can migrate through some or all of the outer layers. Polyps are abnormal growths of tissue that emerge from the lining of the colon and rectum. Not all polyps are cancerous. Certain polyps can gradually become precancerous and then cancerous. Adenocarcinomas are responsible for over 95% of all colorectal cancers.
CRC is usually very slow to develop. In many cases, the disease evolves over a number of years as a noncancerous polyp transforms into cancer.
If unchecked, CRC can progress from a local stage (the cancer is contained in the tissue lining the colon and rectum), to a regional stage (the cancer migrates through the lining to impact adjacent tissue or lymph nodes), to a distant stage (the cancer invades other parts of the body such as the lungs or liver).
Excluding skin cancers, colorectal cancer is the third most common cancer diagnosed in men and in women in the United States. The American Cancer Society estimates that about 108,070 new cases of colon cancer and 40,740 new cases of rectal cancer will be diagnosed in 2008.
An estimated 49,960 deaths from colon and rectum cancer are expected to occur in 2008, accounting for 9% of all cancer deaths. Mortaliy rates from colorectal cancer have declined in both men and women over the past two decades with a steeper decline in the most recent time period (1.8% per year from 1985 - 2002 compared to 4.7% from 2002 - 2004). This decrease reflects declining incidence rates and improvements in early detection and treatment.1
1Colorectal Cancer Facts & Figures, 2008, the American Cancer Society.