Estrogens are well known as the most important and ubiquitous steroid hormones in the female body and are responsible for sexual and reproductive development1. There are three major forms of estrogen (estrone (E1), estradiol (E2) and estriol (E3)) that occur naturally in women. Estrone (E1), which is predominantly found in postmenopausal women, is produced by the conversion of androstenedione via the enzyme aromatase2[3]. The levels of circulating estrogens, including estrone (E1) and estrone sulfate, are positively associated with the development and growth of breast cancer in postmenopausal females. Breast cancer risk increased with increasing body mass index (BMI) (P(trend) =0.002), and this increase in relative risk (RR) was substantially reduced by adjustment for serum estrogen concentrations. Adjusting for free estradiol reduced the RR for breast cancer associated with a 5 kg/m2 increase in BMI from 1.19 (95% CI = 1.05 to 1.34) to 1.02 (95% CI = 0.89 to 1.17). The increased risk was also significantly decreased after adjusting for other estrogens, including total estradiol, non-sex hormone-binding globulin-bound estradiol, estrone, and estrone sulfate[4].
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