Colorectal carcinoma among ethnic Chinese in Singapore -: Trends in incidence rate by anatomic subsite from 1968 to 1192

BACKGROUND. Recent epidemiologic studies have suggested that the distribution of colorectal carcinoma may have undergone a distal to proximal over several decades, which has been attributed variously to environmental and genetic factors as well as preventive intervention. METHODS. Trends in subsite distribution and the incidence rate of colorectal carcinoma among Chinese in Singapore between 1968 and 1992 were explored using data from the Singapore Cancer Registry (n = 10,489). Age-standardized incidence rates were computed and compared further using age-period-cohort models by subsite and gender. RESULTS. The proportion of lesions in the distal colon was found to have increased from 23.2% to 24.4% whereas that for the proximal colon and rectum were fairly consistent over the past 25 years. Our results also showed that age-standardized rates have doubled in proximal lesions (2-3% annually) and more than doubled in distal lesions (3-4% annually) whereas rates in rectal carcinoma have shown a slight increase or stability over time. The patterns of change in all subsite tumors could be attributed to a significant birth cohort effect. CONCLUSIONS. The results of the current study suggest that incidence rates have increased rapidly with no distal to proximal shift observed among ethnic Chinese in Singapore over the past 25 years. The pattern of change differs from findings reported in high incidence countries such as the U.S. and parts of Europe, suggesting that the preventive intervention and early diagnostic capabilities that may have played an important role in these countries have had less effect in Asia. The rapid overall increase in the incidence rate of colon carcinoma supports the role of dietary and other environmental factors as possible risk factors. Cancer 1999;85:2519-25. (C) 1999 American Cancer Society.