Impact of lifestyle and environmental factors on the incidence trend of major cancers for men in Taiwan.

B178

We have recently demonstrated that the incidence of oropharyngeal carcinoma (ICD9 code 140-149 excluding 142 and 147) in Taiwan increased rapidly in the last two decades, while that of nasopharyngeal carcinoma (code 147) decreased in the same period of time. Lifestyle factors, including betel quit use and exposure of other environmental toxins, was considered the most important contributing factor for this phenomenon. Here we extended our study of the cancer incidence trends to other major cancers for men in Taiwan by using age-period-cohort analysis. Epidemiological data of liver (ICD9 code 155), colorectal (code 153/154), and stomach (code 151) cancers from 1981 to 2000 were obtained from the Taiwan Cancer Registry. The calendar time period 1986-1990 and the 1931-1940 birth cohort were used as reference groups for estimates of relative risk. The age-adjusted incidence rates of liver, colorectal, and stomach cancers per 100,000 men were 16.68, 13.36, and 20.84 in 1981 and 51.89, 35.79, and 18.58 in 2000, respectively. Significant cohort effect, but no period effect, was found in the decrease of stomach cancer incidence. The 1911-1920 and the 1966-1975 birth cohorts had a relative risk of 1.42 (95% CI 1.34 - 1.51) and 0.72 (95% CI 0.53 - 0.97), respectively, compared with the 1931-1940 cohort. This trend was similar to that we have found in the incidence of nasopharyngeal carcinoma in Taiwan, suggesting common lifestyle or environmental risk factors for these 2 cancers. Both cohort effect and period effect were found in the incidence trends of liver and colorectal cancers. The relative risk of for the 1966-1975 cohort was 4.22 (95% CI 3.61 -4.94) and 2.52 (95% CI 2.06 - 3.09) for liver and colorectal cancers, respectively, compared with the reference cohort. The relative risk of the 1996-2000 time period was 1.66 (95% CI 1.59 - 1.74) and 1.71 (95% CI 1.63 - 1.80) for liver and colorectal cancers, compared with the reference period. Increase in hepatitis C-related hepatocellular carcinoma was considered the most important cause for the increase in liver cancer incidence for men in Taiwan, while other lifestyle factors may be responsible for the incidence trend of colorectal cancer.