Authors: Greendale GA, Reboussin BA, Slone S, Wasilauskas C, Pike MC, Ursin G.
Publication Year: 2003
Citation: J Natl Cancer Inst 2003; 95(1):30-7.
Breast cancer risk independently increases with mammographic density. Use of hormone replacement therapy (HRT) postmenopausally is associated with an increase in mammographic density, but the extent of the density increase is unknown. This study evaluated mammograms from 571 of the 875 women enrolled in the PEPI trial at baseline and after 12 months HRT. The women had been randomized to receive placebo, conjugated equine estrogens (CEE) + medroxyprogesterone acetate (MPA) in a continuous or cyclic fashion, or CEE + micronized progesterone (MP). Mammograms were analyzed digitally and a linear regression analysis was utilized to quantify breast density change in all four treatment arms. The adjusted absolute mean changes in mammographic percent density over 12 months were 4.76% (95% confidence interval [CI] = 3.29% to 6.23%), 4.58% (95% CI = 3.19% to 5.97%), and 3.08% (95% CI = 1.65% to 4.51%) for women in the CEE+MPA-cyclic, CEE+MPA-continuous, and CEE-MP groups, respectively. Each of those absolute mean changes was statistically significantly different from the adjusted absolute mean change in mammographic percent density for women in the placebo group, which was -0.07% (95% CI = -1.50% to 1.38%). Greater mammographic density was associated with the use of estrogen/progestin combination therapy, although the micronized progesterone containing arm appeared to induce a smaller increase that that with MPA.