Variations in Incidence Within Countries: Epidemiology of Colorectal Cancer

Ethnic Origin

In the United States in the period 1973–1997, the incidence and mortality due to large bowel cancer was higher in blacks than in other ethnic groups (15). The incidence in blacks in the United States is substantially higher than in Africa (3). In England and Wales in the period 1970–1985, the death rate due to large bowel cancer in people born in the Caribbean and East Africa was about half that of those born in England and Wales (21). Nevertheless, this would suggest a higher incidence than in the populations from which they originated. Death rates from the disease in those born in West Africa were similar to those born in England and Wales. These data from the United Kingdom contrasts with those from the United States, but there are differences in the pattern and circumstances of settlement and study period.

As regards other ethnic groups in the United States, in men in the period 1973–1997, the incidence was lower in Asian/Pacific Islanders than in white males, and lower again in Hispanic and Native Americans and Alaskan Natives than in Asian/Pacific Islanders (15). Among women incidence rates were similar for Asian/Pacific Islanders, Hispanics and Native Americans, and Alaskans, and were lower than the levels observed in white and black women.

In addition to levels of incidence varying by ethnic group, there are some differences in time trends. In the United States while incidence has been declining in the white population since the mid-1980s, this trend has not been seen in the black population (15).

Socioeconomic Status
In most countries, the risk of colon cancer has been found to be higher in those with higher socioeconomic status (22). This has been observed in both men and women, both for incidence and mortality, and for diverse measures of socioeconomic status. The increase in risk with increasing socioeconomic status contrasts with most other types of cancer. No consistent association between cancer of the rectum and socioeconomic status has been observed.

Survival and Mortality: International Variations and Time Trends
In developed countries, colorectal cancer death rates have declined steadily over the past 20 to 30 years (23). This is due, at least in part, to declining proportions of patients presenting with more advanced disease over time (24,25), and most likely a consequence of increased availability and use of sigmoidoscopy, colonoscopy and, possibly, fecal occult blood (FOB) testing.

The extent of disease at diagnosis is a strong predictor of survival for both colon and rectal tumors. USA Surveillance, Epidemiology and End Results (SEER) Program data for patients diagnosed with colon cancer in 1992–1997 show five-year relative survival of 91% for those whose disease was localized at diagnosis, 67% for those presenting with regional spread, and 9% for those with distant metastasis (15). For rectal cancer the corresponding figures were 87%, 57%, and 8%. Of all those for whom the extent of disease was known, 39% had localized disease, 40% regional spread, and 21% distant metastasis.

In most of western and northern Europe, survival is lower than in the United States (26). This difference may be heavily influenced by a higher proportion of colorectal cancers that are adenocarcinomas in polyps diagnosed in the United States than in Europe (27).

Rebecca A. Barnetson and Malcolm G. Dunlop
Colon Cancer Genetics Group, University of Edinburgh, School of Molecular and Clinical Medicine and MRC Human Genetics Unit, Western General Hospital, Edinburgh, U.K.


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