Colorectal cancer incidence among Chinese in North America and the People's Republic of China: variation with sex, age and anatomical site.

Age-specific incidence rates for cancers of the colon and rectum are presented for Chinese in the western United States and Canada (high risk area), and in Shanghai, the People's Republic of China (low risk area). These rates are compared to those among North American whites. Among Chinese, rate differences between high and low risk areas are greater for colon cancer than rectal cancer, are greater for men than women, and increase with age. The most striking finding is the high colon cancer incidence among older Chinese-American men, compared to Chinese-American women. Colon cancer rates among elderly Chinese-American men equal those of whites, which are seven times the corresponding rates in China. By contrast, colon cancer rates among older Chinese-American women are intermediate between those of whites and those in China, and are only three to four times the rates in China. Rectal cancer rate differences for Chinese men also exceed those for Chinese women. However, they are less dramatic than for colon cancer, with elderly Chinese-American men having roughly double the rates in China, and with women exhibiting little variation between continents or ethnic groups. Male:female (M:F) rate ratios increase with age for both continents, both ethnic groups, and both colon and rectum. The colon cancer M:F ratios among Chinese-Americans exceed the others, reaching two in the older age groups. These observations suggest sex-specific aetiological exposures, or sex-specific susceptibilities to common exposures, among Chinese-Americans.(ABSTRACT TRUNCATED AT 250 WORDS)