Serum sex hormone levels after menopause and subsequent breast cancer.
BACKGROUND: High levels of androgens and estrogens have been reported to be associated with breast cancer. However, the multiplicity of factors that influence hormone levels and methodologic issues complicate the study of the relationship between steroid sex hormones and breast cancer. PURPOSE: Using an improved study design, we assessed prospectively the relationship between the principal steroid sex hormones in serum and the subsequent occurrence of invasive breast cancer in postmenopausal women. METHODS: Four thousand fifty-three healthy postmenopausal women aged 40-69 years, were enrolled from June 1987 through June 1992 in a prospective investigation of hormones and diet in the etiology of breast tumors (ORDET study) as part of a larger volunteer cohort of 10 788 premenopausal and postmenopausal women from Varese Province, northern Italy. At recruitment, blood samples were taken between 8:00 AM and 9:30 AM (after overnight fasting), and sera were preserved in -80 degree Celsius freezers. Women who had received hormone treatment in the 3 months prior to enrollment, who had bilateral ovariectomy, or who had a history of cancer or liver disease were not recruited. Twenty-five women in the final eligible cohort of postmenopausal women developed histologically confirmed, invasive breast cancer during the first 3.5 years of follow-up for the cohort (13 537 women-years). For each case subject, four control subjects were randomly chosen after matching for factors possibly affecting hormone preservation in serum. One case subject and eight control subjects were excluded because premenopausal hormonal patterns were found; thus, after also excluding the four control subjects matched to the ineligible case subject, we included 24 case and 88 control subjects. In the spring of 1994, stored sera of case and control subjects were assayed in a blinded manner for dehydroepiandrosterone sulfate and estradiol (E2) by in-house radioimmunoassay and for total and free testosterone and sex hormone-binding globulin by commercially available nonextraction iodination kits. Mean differences in risk factors were tested by analysis of variance for paired data. Relative risks (RRs) were estimated by conditional logistic regression analysis. All P values resulted from two-sided tests. RESULTS: Age-adjusted mean values of total testosterone, free testosterone, and E2 were significantly higher in case subjects than in control subjects: total testosterone, 0.34 ng/mL versus 0.25 ng/mL (P<.001); free testosterone, 1.07 pg/ml versus 0.77 pg/mL (P= .006); and E2, 25 pg/mL versus 22 pg/mL (P= .027). Age-adjusted RRs for breast cancer in increasing tertiles were as follows: for total testosterone, 1.0, 4.8, and 7.0 (P for trend =.026); for free testosterone, 1.0, 1.8, and 5.7 (P for trend=.005); and for total E2, 1.0, 7.1, and 5.5 (P for trend= .128). CONCLUSIONS AND IMPLICATIONS: This prospective study provides further evidence in support of the already established association between elevated estrogen levels and breast cancer. Even more importantly, it provides new evidence that high serum testosterone levels precede breast cancer occurrence.