An association between sex steroids and mammographic density (MD), a predictor of breast cancer (BC) risk, is supported by findings of increased densities after hormone therapy and reduced densities after tamoxifen treatment. Herein, ethnic differences in urinary hormone levels and their relation to MDs were investigated. Because 2-hydroxyestrone (2-OH-EO is considered less carcinogenic than 16a-hydroxyestrone (16a-OH-Ei), we hypothesized an inverse relation between the ratio and breast densities. Women recruited completed a questionnaire and donated urine during the luteal phase. Urinary estrone (E,), estradiol (E2), testosterone (T), and 5a-androstane-3a, 17p-diol (ADIOL) were measured by indirect radioimmunoassay (RIA) and by competitive immunoassays. MDs were assessed with a computer-assisted method and applied multiple linear regressions. The total number of subjects was 305 (35-75 years, x = 47.2 years). Their ethnic distribution was Caucasian (110), Japanese (86), Hawaiian (35), Chinese (28), and mixed/other ethnicity (46). The data indicate that the body mass index (BMI), androgens (A), total hormones, and the 2/16 ratio were significantly lower in Asians than in Caucasians, but the % MDs were 22% higher in Asians. None of the individual hormones was associated with MDs. However, contrary to the initial hypothesis, the 2/16 ratio was directly related to MDs. The ratio was 25% lower in the lowest MD category as compared to the highest category. The data suggest that the effects ofendogenous hormones on BC risk may not be mediated through MDs in adult women.

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