EFFECT OF ESTROGEN AND ESTROGEN-PROGESTIN REPLACEMENT REGIMENS ON MAMMOGRAPHIC BREAST PARENCHYMAL DENSITY

Purpose: Hormone replacement therapy (HRT) may increase the mammograph ic density with a possible reduction in the sensitivity or specificity , If so, the benefit of mammographic screening in women using HRT coul d be compromised, We evaluated the hypothesis that HRT regimens have d ifferential effects on the mammographic density depending on treatment regimens ol on age. Patients and Methods: Among 31,498 Swedish women who received mammographic screening, we selected 554 women who started HRT after the first examination and who were current users at the sec ond, and 554 age-matched women who had never received HRT. Mammograms were examined in a blinded review, The changes in density between the two examinations, graded as moderate or weak reduction, no change, or weak, moderate, or substantial increase, were assessed, We studied fou r HRT regimens-estradiol compounds only, estradiol compounds cyclicall y or continuously combined with progestins, and weak estrogens-and use d descriptive statistics and logistic regression to analyze the associ ation between HRT and density change. Results: Density increased in 10 % and 28% of women who received estradiol compounds with cyclically or continuously combined progestins, respectively, but in only 3% of une xposed women. Logistic regression analyses showed an elevated risk of a density increase (relative risk [RR] = 3.6; 95% confidence interval [CI], 1.6 to 7.7) in women who received cyclically combined regimens o r continuously combined regimens (RR = 12.4; 95% CI, 6.3 to 24.4) comp ared with unexposed women, Women greater than or equal to 50 years of age had even stronger associations; RRs in women on estradiol only, th e cyclically combined and the continuously combined regimens were 32.2 (95% CI, 3.9 to 267.5), 21.9 (95% CI, 1.9 to 251.5), and 176.9 (95% C I, 22.8 to 1,372.7), respectively. Conclusion: HRT with estradiol-prog estin regimens, especially continuously combined, may increase the mam mographic density in ct substantial proportion of women. (C) 1997 by A merican Society of Clinical Oncology.