Impact of lifestyle and environmental factors on the incidence trends of major cancers for women in Taiwan.

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We have recently demonstrated that the breast cancer (ICD9 code 174) incidence for young women in Taiwan is rapidly increasing and approaching that of Caucasian women of the same generation. Westernization of lifestyle 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 women in Taiwan by using age-period-cohort analysis. Epidemiological data of liver (ICD9 code 155), colorectal (code 153/154), lung (code 162), stomach (code 151), and invasive uterine cervical (code 180.3) 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. Invasive cervical cancer was the only cancer whose incidence decreased in this period of time. The age-adjusted incidence rate of invasive cervical cancer was 28.41 per 100,000 women in 1981 and 23.73 in 2000, respectively. Among others, liver cancer had the fastest increase in incidence. The incidence for liver, breast, colorectal, lung, and stomach cancers were 3.44, 14.0, 10.15, 7.90, and 8.16 per 100000 women in 1981 and 19.9, 39.60, 27.92, 18.31, and 10.46 in 2000. Decrease in the incidence of cervical cancer occurred before the widespread use of Pap smear screening in Taiwan, and significant cohort effect was found. The 1966-1975 birth cohort had a relative risk of 0.69 (95% CI 0.58 - 0.83) compared with the 1931-1940 cohort. No significant period effect was noted. Among others, breast cancer has the greatest cohort effect. The relative risk of for the 1966-1975 cohort was 6.57 (95% CI 5.72 - 7.55), 4.82 (95% CI 3.52 - 6.59), 3.07 (95% CI 2.47 - 3.81), 2.14 (95% CI 1.49 - 3.07), and 0.90 (95% CI 0.68 - 1.18) for breast, liver, colorectal, lung, and stomach cancers, respectively. On the other hand, liver cancer had the greatest period effect. The relative risk of liver cancer for the 1996-2000 time period was 2.19 (95% CI 2.01 - 2.38) compared with the 1981 - 1985 period. Increase in hepatitis C-related hepatocellular carcinoma was considered the most important cause for the rapid increase in liver cancer incidence for women in Taiwan. Increasing westernization of lifestyle, including change of diet habit, better sanitation, and decrease exposure to potential environmental hazards may be responsible for the incidence trends of other major cancers in Taiwan.