Risk Factors for Breast Cancer: A Case-Control Study from Taegu, Korea

Abstract

A hospital-based case-control study was carried out to identify reproductive risk factors for breast cancer in Taegu, Korea. Four hundred and eighty-one breast cancer patients and 491 age-matched control patients examined between 1988 and 1994 were included in this study. Eleven reproductive risk factors were selected for comparison using cross tabulation and chi-square method, and univariate and multivariate logistic regression analyses were used to evaluate the odds ratios for the risk of breast cancer. The mean age of the breast cancer patients in this study was 47.5 years. Analyses demonstrated that nulliparous women had a higher risk for breast cancer (odds ratio 3.46, p = 0.03) than women with one to four live births, and women who had an abortion during their first pregnancy had a slightly increased risk (odds ratio 1.86, p < 0.01) than women who had normal deliveries, but the age at menarche and menopause did not have any influence on the risk of developing breast cancer. Although there were similarities in risk factors between Western women and women in this study, such as a higher risk for nulliparous women, two key factors were found to contrast with those of Western women. First, the mean age of breast cancer patients in this study was only 47.5 years. Second, the age of menarche and menopause of these women did not have any influence on the risk of breast cancer. any risk factors for breast cancer have been M found and many of them are recognized as established factors, at least in the Western hemisphere. Reproductive factors and the patient's age are probably among the most important risk factors. Shapiro and coworkers (1) in 1968 reported that excess of breast cancer occurred in women who had never been married, those who had no more than two pregnancies, those with an early menarche, and those with 30 or more years of menstrual activity. Then in 1970, by a seven-center collaborative study of MacMahon and co-workers (2), a late age at first full-term birth became a major reproductive risk factor for breast cancer. The relationship between age and breast cancer risk was first described by Clemmesen in 1948 (3). In the United States and most European countries, the risk of breast cancer increases rapidly with age during childbearing years and the rates continue to increase even after menopause although at a less rapid pace.Accumulated data also suggests that there are international geographic variations in the incidence and mortality rates of breast cancer (4). Due to the fact that the incidence rate of breast cancer for Korean women was reported to be 9.9 per 100,000 (5), perhaps the lowest in the world, it is reasonable to assume that risk factors might be different for Korean women than those reported for women in the Western hemisphere. We carried out a hospital-based case-control study to identify reproductive risk factors for breast cancer in Taegu, Korea. Although the cases selected here may not be representative of all Korean women, the risk factors we may