Note: Some citations in the text of this section are followed by a level of evidence. The PDQ editorial boards use a formal ranking system to help the reader judge the strength of evidence linked to the reported results of a therapeutic strategy. (Refer to the PDQ summary on Levels of Evidence for more information.)
Deaths: 49,380 (colon and rectal cancers combined).
It is difficult to separate epidemiological considerations of rectal cancer from those of colon cancer because epidemiological studies often consider colon and rectal cancer (i.e., colorectal cancer) together.
Worldwide, colorectal cancer is the third most common form of cancer. In 2000, colorectal cancer accounted for 9.4% of the world's new cancers, with 945,000 cases diagnosed, and 7.9% of the world's cancer deaths, with 492,000 deaths. Colorectal cancer affects men and women almost equally. Among all racial groups in the United States, African Americans have the highest sporadic colorectal cancer incidence and mortality rates.[3,4]
Adenocarcinomas account for the vast majority of rectal tumors in the United States. Rare tumors, including carcinoid tumors, lymphomas, and neuroendocrine tumors, account for less than 3% of colorectal tumors.
The rectum is located within the pelvis, extending from the transitional mucosa of the anal dentate line to the sigmoid colon at the peritoneal reflection; by rigid sigmoidoscopy, the rectum measures between 10 cm and 15 cm from the anal verge. The location of a rectal tumor is usually indicated by the distance between the anal verge, dentate line, or anorectal ring and the lower edge of the tumor, with measurements differing depending on the use of a rigid or flexible endoscope or digital examination. The distance of the tumor from the anal sphincter musculature has implications for the ability to perform sphincter-sparing surgery. The bony constraints of the pelvis limit surgical access to the rectum, which results in a lesser likelihood of attaining widely negative margins and a higher risk of local recurrence.
Genetic risk factors
Individuals with certain known single-gene disorders are at an increased risk of developing rectal cancer. Single-gene disorders related to known syndromes account for about 10% to 15% of colorectal cancers. (Refer to the PDQ summary on Genetics of Colorectal Cancer for more information.) The hereditary colorectal cancer syndromes and some genes that are involved include:[7,8,9]