Epidemiologic characteristics of cancer of the breast in Taiwan

An attempt was made to identify and interview all cases of breast cancer diagnosed during a 3-year period in the population of a defined area of Northern Taiwan; 232 cases were identified, and 213 were interviewed. For comparison, similar interviews were conducted with 648 patients with diseases other than breast cancer. Mortality data for Taiwan as a whole have also been used in certain analyses. The average annual incidence rate in the study area was 6.11 per 100,000 female population. Age-specific incidence rates show a pattern similar to that noted in Japan and in the Chinese population of Singapore, rates plateauing in middle-age and then declining in the older age groups. However, mortality rates show a consistent increase with age throughout the life span. There was no evidence of an increase or decrease in mortality rates over the decade 1954-1963. Mortality and incidence rates were both substantially higher among persons born in mainland China than among nativeborn Taiwanese. Risk of breast cancer was sharply lower in women of parity 1 than in nulliparous women, and in women of parity 2 than in those of parity 1. There was no further appreciable decline with increase in parity higher than parity 2. Association with parity was particularly marked for women whose breast cancer was diagnosed after 50 years of age. There was no significant or consistent difference between cases and controls with respect to any of several measures of lactation experience. There was a tendency towards earlier menarche and later menopause in the cases than in the controls, but the differences were not significant. A strong and significant association with weight was found, women weighing more than 55 kg having more than twice the breast cancer risk of those weighing less than 45 kg. There was no consistent or significant association with height. In general, these findings are similar to observations made both in Japan and in high risk areas, but the data from Taiwan are unusual in showing a strong relationship to parity and only a weak association with age at first pregnancy.