Beattie MS, Costantino JP, Cummings SR, et al. Endogenous sex hormones, breast cancer risk, and tamoxifen response: An ancillary study in the NSABP breast cancer prevention trial (P-1). J Natl Cancer Inst. 2006; 98(2):110-115.

The endogenous sex hormone levels of some women at high-risk for breast cancer may paint a false picture of that risk, according to a recent study. Investigators measured estradiol, testosterone, and sex hormone-binding globulin in plasma samples taken from a study group of 135 women with postmenopausal breast cancer and 275 postmenopausal women without breast cancer who served as controls in the National Surgical Adjuvant Breast and Bowel Project Cancer Prevention Trial. Women had received tamoxifen or placebo for 69 months. Median plasma levels of estradiol, testosterone and sex hormone-binding globulin were similar in study patients and controls. Relative risk for breast cancer in women with sex hormones in the highest quartile was 1.29 compared with those in the lowest quartile-an insignificant difference between the lowest and highest quartiles.

Although this study was the first to examine breast cancer risk and sex hormones in a high-risk population, the clinical implications are in line with previous studies.