Breast Cancer Risk Factors in Two Distinct Ethnic Groups: Indian and Pakistani vs. American Premenopausal Women

Abstract

Asian Indians from the Indian subcontinent have low rates of breast cancer, but studies on breast cancer risk factors in Indian and Pakistani women living in the United States are lacking. This study contrasted breast cancer risk factors [serum total 17β-estradiol (E₂), sex hormone-binding globulin-bound E₂, available E₂, estrone (E₁), and dehydroepiandrosterone sulfate, reproductive history, family history of cancer, body composition/size, dietary intake, physical activity, and excretion of isoflavones] between two distinct ethnic groups of premenopausal women residing in the United States. We also determined the contribution of these and other factors to the variability of each sex hormone. Distributions of values for serum total E₂, available E₂, and sex hormone-binding globulin-bound E₂ (%) were greater (p < 0.005) in American (n = 47) than in Indian and Pakistani (n = 47) women. Multiple regression analysis indicated that 26% of the variability (p <.0001) in serum E₂ was accounted for by the ratio of total cholesterol to high-density-lipoprotein cholesterol, length of time in the United States, and saturated fat intake, whereas less (17%) variability was accounted for by available E₂ (representing free E₂ + albumin-bound E₂;), contributed by the ratio of total cholesterol to high-density-lipoprotein cholesterol and saturated fat intake. Five variables accounted for 31% of the variability (p <.0001) in E₁. The major finding of this study was that circulating sex hormone concentrations were determined more by environmental factors than by ethnicity, which was not a significant contributor to any of the serum hormones.