[MOL] Risks Factors for Colon and Rectum Cancers [01929] Medicine On Line

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[MOL] Risks Factors for Colon and Rectum Cancers

Colon and Rectum

Arthur G. Schatzkin, M.D., Dr. P.H.*

Together, the colon and rectum make up the large bowel, or large intestine. The colon refers to the upper five or six feet of the large intestine, the rectum to the last five or six inches. Because of the anatomic and physiologic similarity of tissue in the colon and rectum and the occasional difficulty in determining in which region a tumor has arisen, malignancies in these two bowel segments are often lumped together as "colorectal cancer."

Fifty-six thousand colorectal cancer deaths are estimated to have occurred in the United States in 1994 (Boring et al., 1994). It is the second leading cause of cancer death in the U.S. population as a whole, second among men and third in women. Approximately 149,000 new cases of colorectal cancer were projected for 1994, representing nearly 15 percent of all cancers diagnosed that year in this country. Colorectal cancer ranks second in cancer incidence for the combined U.S. population. Among men this is the third most commonly occurring malignancy (after prostate and lung cancers); among women it ranks third (after cancers of the breast and lung).

Five-year survival from this malignancy has improved somewhat over the past 20 years, and for patients diagnosed during 1983 through 1990, was 58 percent (Ries et al., 1994).

The incidence of colorectal cancer, as with many malignancies, is extremely low in childhood, increasing dramatically with age. SEER data for 1987-91 show, for example, that the incidence of the disease in persons 75-79 was 391/100,000; for those aged 50-54, the rate was only 51/100,000 (Ries et al., 1994). The median age at diagnosis of colorectal cancer in the United States is 70 for men and 73 for women. (Comparable median ages at diagnosis for other cancers are 63 for breast in women and 67 for lung in men.) The overall incidence of colorectal cancer is higher in men (58.9/100,000 in 1987-91) than in women (40.4/100,000), and this holds for all age groups.

Total incidence rates are comparable for whites (47.8/100,000) and blacks (52.4/100,000) (Ries et al., 1994). Rates are similar for white (58.7/100,000) and black (60.9/100,000) men, but slightly lower for white (39.9/100,000) compared to black (46.7/100,000) women. Incidence rates among blacks have caught up with those in whites over the last 15 years. Mortality rates are slightly higher in blacks than whites for both men and women.

In general, colorectal cancer rates, unlike those for cancers of the lung, cervix, and prostate, for example, show little socioeconomic gradient in the United States and other developed countries. In the United Kingdom, the elevated large intestinal cancer mortality in Social Class I (upper class) that was present at the turn of the century had essentially disappeared by 1970 (Logan, 1982). In contrast, data from Cali, Colombia (Haenszel et al., 1975), with an overall colorectal malignancy incidence much lower than that in developed countries, show a substantial excess of large bowel cancer in the upper socioeconomic strata, whose members tended to have lifestyle, including dietary, characteristics typical of more industrialized nations.

Colorectal cancer incidence and mortality vary at least ten-fold between countries with the highest and those with the lowest rates (Kurihara et al., 1984; Whelan et al., 1990). The highest incidence and mortality rates are seen in the more industrialized countries of North America, Northern and Western Europe, and New Zealand; the lowest rates are in Asia and Africa.

A rapid rise in colorectal cancer rates in a particular area signals the action of environmental factors. Such a rapid increase has been observed in Japan, where from 1969 to 1981 colorectal cancer mortality increased 44 percent in men and 40 percent in women (Kazuo et al., 1985). In the United States, from 1973 to 1991, the incidence of colorectal cancer increased 12.3 percent among men but decreased by 2.0 percent in women (Ries et al., 1994).

Numerous studies in migrants show a general convergence in colorectal cancer rates from the country of origin to the country of destination (Ziegler et al., 1985). For example, in a recent study from Australia, large bowel cancer mortality increased for persons coming from certain countries like Greece and Yugoslavia (McMichael and Giles, 1988) where rates had previously been lower. Especially noteworthy in these Australian findings is the relatively rapid convergence in colorectal cancer rates within the life span of the migrants.

In line with the evidence cited above, dietary intake varies considerably across countries, has changed over time in countries like Japan, and may be altered substantially during acculturation following migration. Moreover, food (or its various metabolites) affects several potentially important intestinal processes and comes into direct contact with gastrointestinal epithelial tissue (Bruce, 1987).

Animal experiments have shown dietary fat to promote large bowel tumors (Reddy, 1983). The international correlation between per capita fat consumption and colorectal cancer rates is very strong (Draser, 1973). Epidemiologic studies have generally shown a direct association between fat intake and colorectal cancer risk. In a prospective cohort study of approximately 90,000 nurses, investigators found that women in the highest of five categories of daily animal fat intake, compared to those in the lowest category, had nearly twice the risk of developing colon cancer (Willett et al., 1990). Evidence indicates that most colorectal cancers originate as benign growths of the intestinal lining, called adenomatous polyps. In a recently reported investigation of male health professionals with adenomatous polyps, men in the highest category of dietary fat intake had twice the risk of adenomatous polyps as those in the lowest quintile (Giovannucci et al., 1990).

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