This cancer represents the second most common internal malignancy in the United States, after cancer of the lung. In 1995 there were 155,000 cases of colon-rectal carcinoma, and about 61,000 deaths. 
The peak incidence is in the sixth decade, which means after age 50, but some cases have been observed in patients younger than 40. 

The distribution of cancer of the rectum varies in different segments of the colon, also known as the large bowel : the most distal part, which consists of the rectum and the sigmoid colon, is more prone to develop cancer than the proximal part, which is on the right side of the abdomen. In the most recent years, however, cancers on the right side of the colon are becoming increasingly more common. 

Interestingly enough, there are differences in incidence between ethnic groups, white americans have a higher incidence than african americans; also with respect to religion, for example Jews in the United States have a higher incidence than the average population, while Mormons and Seven Day Adventist have a much lower rate then the general population. This has been attributed to dietary habits, mostly concerning the use of tobacco, alcohol and red meats. 

While the immediate cause of colo-rectal cancer is unknown, many factors have been considered of some importance, the genetic factor being probably the most significative. Recently researchers at Johns Hopkins Hospital have identified some of the genes that are considered responsible for the development of colon and rectal cancer. It is known that first degree relatives of patients with carcinoma of the colon and rectum have a much higher risk than the general population to develop the disease. The increased risk is difficult to quantify, but it may be twice as high if one relative is affected and ten times if two family members are affected. The risk is even higher in familial conditions such as familial polyposis and Lynch syndrome (also known as Non Polyposis Familial Colorectal Cancer Syndrome). 

Dietary factors are also extremely important. Population with diets high in fat and protein, especially if associated with low fiber ingestion, are at higher risk of developing carcinoma of the colon and rectum. The type of fat is also extremely important. Olive oil, coconut oil and fish oil do not increase the incidence of colon carcinoma, while beef fat increases the risk of colon cancer. A diet that is high in fibers seems to have a protective effect against the development of colon cancer. 

Vitamins and micro elements have raised some hopes:some reports have been published and raised public hope that prevention could also be increased by the intake of vitamins A,C,E, a different variety of vegetable products. The clinical application of these products needs to be evaluated and should not be used in an dangerous fashion. 

Most of the colon and rectal cancers start as benign neoplasms, known as polyps. 

The polyp-cancer sequence is now an accepted concept that has scientific validity and is based on several undisputable observations. This concept is extremely important since early detection and complete removal of colon and rectal polyps would prevent the development of most of the cancers of the colon and rectum. These goals are achieved by screening the population before symptoms appear. The most common screening tools are stool test for occult blood, air contrast barium enema, flexible sigmoidoscopy and colonoscopy. 

The symptoms of colon and rectal cancers are both nonspecific and late. The presence of bleeding, change in bowel habits, abdominal pain and discharge of mucus should alert the patient and require a physicians immediate attention. 

Treatment of cancer of the colon and rectum used to be considered purely surgical. Today it involves a combination of surgery with radiation therapy and/or chemotherapy. 

The use of radiation therapy either before or after the surgery is usually limited to cancers of the rectum. 

Chemotherapy, given as a adjuvant to the surgical therapy has been widely recommended to more advanced variety of cancers of the colon and rectum. 

The use of the newer agents for chemotherapy has been associated with very little side effects, such as hair loss, nausea and vomiting.