Cancers of the colon and cancers of the rectum have much in common, but there are some differences in risk factors, morphology, and treatment. The colon and rectum are parts of the digestive tract and together they form the large intestine (or large bowel). The colon absorbs water and some vitamins from the partially digested food delivered by the small intestine. The rectum stores feces until it is eliminated through the anus. The colon is the first approximately five feet of the large intestine and the rectum is the last several inches. The colon is a large organ comprised of several named parts, but a division into two sections is useful when describing the distribution of colon cancer in Indiana. The right or proximal colon, which includes the appendix, is in the right half of the abdomen and is the part of the colon to which the small intestine joins. The left or distal colon ends with the sigmoid colon, which joins the rectum. When referring to cancer of either primary site (colon or rectum), the term, colorectal cancer, is often used. (The primary site is the location in the body where the cancer began.)
Tumors (also called neoplasms) are described not only by their site of origin, but also by the type of cells involved (histology) and by their behavior. The behavior of a tumor can be benign (not cancer) or malignant (cancer). Benign tumors may grow in size but will not invade other tissues; they are rarely life-threatening. Malignant neoplasms frequently grow rapidly, the cells invade (grow into) other tissues, and they may metastasize (spread to other sites that are not adjacent to the site of origin).
The most common histology of colorectal cancers is adenocarcinoma. For 2003, adenocarcinoma represented 93% of all colorectal cancers diagnosed in Indiana residents, a percentage that matches the US average of 90 - 95%. Carcinoid tumors, the next most common histology for colorectal cancers, were just 2% of all cancers of the colon and rectum in Indiana. Most malignant tumors diagnosed in 2003 were located in the left or distal colon (55%); whereas, the right or proximal colon was the site for approximately 39% of colorectal cancers. In Indiana, over 50% of carcinoid tumors diagnosed in 2003 were located in the rectum. Squamous cell carcinomas were found only in the rectum and represented 0.1% of the colorectal cancers diagnosed in Indiana in 2003.
Colorectal cancer was newly diagnosed in 3,369 residents of Indiana in 2003. Colorectal cancer accounts for 11.6% of all newly diagnosed cancers in the state. There were 2,499 new cases of colon cancer and 870 new rectal cancer cases. (Table 4.2) Excluding skin cancer (the most common cancer), colon cancer is the third most frequently diagnosed cancer in men, women, and both sexes together. Compared with the entire United States, Indiana’s colon cancer incidence rate* was statistically significantly higher (40.0 newly diagnosed cases per 100,000 Indiana residents versus 35.5/100,000 US residents) over the 5-year period from 1999 to 2003. (Table 1-1)
Colorectal cancer is the second leading cause of cancer death for men and women combined and the third leading cause of death for each sex separately. In 2003, there were 1,096 deaths from colon cancer and 174 deaths from rectal cancer. (Table 4-4) The mortality rates were: colon cancer - 17.5 deaths per 100,000 Indiana residents; rectal cancer - 2.8/100,000. (Table 4-3) Over the 5 years from 1999 - 2003, the average annual death rate from colon cancer in Indiana (17.5) was statistically significantly higher than the US rate (17.1). (Table 1-2) This amounts to an excess of about 25 colon cancer deaths per year in Indiana.
Racial and ethnic disparities are apparent in the incidence of colorectal cancer and in colorectal cancer mortality. African-American males are more likely to be diagnosed with colon cancer (59/100,000 in 2003) and/or rectal cancer (20.8/100,000) than are white males (47.5 and 19.9 respectively). African-American females are more likely to be diagnosed with colon cancer (47.1) than are white females (37.1); however, white females are more likely to be diagnosed with rectal cancer (11.2) than are African-American females, though the differences between the rates of rectal cancer for blacks versus whites are not statistically significant.
African-Americans in Indiana are almost 45% more likely to die of colon cancer than are whites. The 2003 mortality rate for blacks was 24.8/100,000, which is statistically significantly higher than the rate for whites (17.2/100,000). African-Americans are less likely to be diagnosed at the local stage when there is the best chance for a cure (5-year survival of 90%), and more likely to be diagnosed at the distant stage with 5-year survival at only 10%.
Hispanics have statistically significantly lower rates of both colon and rectal cancer, for both men and women, than do non-Hispanics. For the 5- year period from 1999 - 2003, the incidence rate of colon cancer was 23.6 for Hispanic males versus 46.9 for non-Hispanic males. The rate of rectal cancer was 13 for Hispanic males and 19.4 for non-Hispanic males. For Hispanic women, the colon cancer incidence rate was 29.8 versus 36.8 for non-Hispanic women. The rate of rectal cancer for Hispanic women was 7.2. (This rate should be considered unstable, as there were less than 20 cases diagnosed for Hispanic women between 1999 and 2003.) The rate of rectal cancer in non-Hispanic women was 10.9 for the same 5-year period.
The 2005 Indiana Behavioral Risk Factor Surveillance System (BRFSS) survey found no statistically significant difference in screening rates for colorectal cancer between whites and blacks, using either the Fecal Occult Blood Test (FOBT) or one of sigmoidoscopy or colonoscopy. The FOBT is a test performed at home that detects hidden blood in the stool, which can be a sign of colon cancer, as well as, many other gastrointestinal diseases. Sigmoidoscopy and colonoscopy are tests in which a flexible, lighted tube with a miniature video camera at the end is inserted through the anus to examine the rectum and colon. Sigmoidoscopy checks the rectum and the lower part of the colon, while colonoscopy examines the rectum and the entire colon. If polyps are found during the examination of the rectum and colon, the doctor removes them. Polypectomy (the removal of polyps) can prevent colorectal cancer, since the majority of colon and rectal cancers originate in adenomatous polyps.
There are a number of factors which increase a person’s risk for colon and rectal cancer. Perhaps, the most important risk factor is age; 90% of colorectal cancers are diagnosed in people over the age of 50. Factors which place an individual at high risk of colorectal cancer are: 1) a personal history of adenomatous polyps or of colorectal cancer, 2) for women, a history of cancer of the ovary, uterus, or breast, 3) a history of colorectal cancer or adenomatous polyps in a first degree relative (parent, brother, sister, son, or daughter) diagnosed before age 55, or in two or more first degree relatives at any age, 4) a personal history of chronic Ulcerative Colitis or chronic Crohn’s colitis, 5) specific gene syndromes, such as, Familial Adenomatous Polyposis or Hereditary Non-Polyposis Colon Cancer. Factors which place an individual at high risk account for approximately 23% of colorectal cancers. There are no risk factors other than age in 75% of cases.
Several lifestyle factors either increase or may increase the risk of developing colorectal cancer. Smoking increases the risk of colorectal cancer 30 - 40%. Diets high in red meat and saturated fats, and low in fruits and vegetables may increase the risk of colorectal cancer, as does lack of adequate physical activity. High alcohol consumption may also increase the risk of colorectal cancer, though the evidence is inconsistent at this time.
Screening Recommendations for Colorectal Cancer for People of Average Risk
Individuals at high risk should speak with their doctors about which screening option is right for them. The physician may recommend starting screening at an earlier age, screening at more frequent intervals, or both.
Colorectal cancer is preventable.
* All rates are per 100,000 people in the at-risk population and are age-adjusted to the US 2000 Standard Population.
