An investigation of soy intake and mammographic characteristics in Hawaii

Based on ethnic [1] and international [2] differences in breast cancer risk, and on results from cell and animal studies [3], a role for soy foods in breast cancer prevention has been proposed. The epidemiologic investigations on soy and breast cancer risk have so far produced conflicting results [4,5,6,7,8,9,10]. Mammographic densities that refer to the distribution of fat, connective, and epithelial tissue in the female breast have been shown to be related to breast cancer risk [5]. A high percentage of dense parenchyma on mammographic images appears to confer a fourfold risk of developing breast cancer [11].The purpose of this report is to investigate the hypothesis that soy foods are related to lower mammographic densities among a population of women with Caucasian, Chinese, Japanese, and Native Hawaiian ancestry living in Hawaii.In a cross-sectional study approved by the institutional review boards of all participating institutions, women with different ethnic backgrounds were recruited at five mammography facilities on the island of Oahu. All study participants signed informed consent and completed a validated food frequency questionnaire (FFQ) [12] especially designed for a multiethnic population [13]. Because the FFQ included only two soy food items, we designed a soy questionnaire (SQ) with 10 categories of soy foods that are commonly consumed in Hawaii: tofu, fried tofu, pressed tofu, green soybeans, miso, soybean sprouts, tofu skin, soy milk/drink, vegetarian meats, and fermented soybeans. Intake of soy foods according to the SQ in a validation study among 102 women was highly correlated with urinary isoflavone excretion [14].Both cranio-caudal views of the mammogram were obtained from the mammography clinics after the radiologic evaluation had been completed and any malignancy or suspicious lesions ruled out. Women who reported a history of breast cancer or augmentation surgery were excluded from the study. Computer-assisted mammographic density assessme