The purpose of this study is to determine whether cessation of hormone replacement therapy for one or two months before a screening mammogram will improve its performance by decreasing breast density.

This randomized, controlled trial is designed to test whether short-term (1-2 months) HRT cessation will sufficiently lower breast density to decrease the proportion of women who receive a recommendation for additional evaluation following a screening mammogram, and to examine whether there is a trend by duration of cessation. The study is being conducted at Group Health Cooperative, a managed health care organization in western Washington State with an organized breast cancer screening program. We are recruiting 1,500 women and will randomize women to one of three HRT arms: 1) cessation two months before the screening mammogram; 2) cessation one month before; and 3) continued HRT use. We are using a computer-assisted method to measure mammographic breast density continuously. Mammography recall rates are being determined from an expert radiologist review of the mammograms, blinded to HRT status.

Inclusion Criteria:

• 1 or more prior screening mammograms at Group Health Cooperative within the past 2 years
• Currently taking HRT
• Taking HRT at prior screening mammogram
• Due for a screening mammogram

Exclusion Criteria:

• BI-RADS breast density of 1 (entirely fat)
• Previous cardiovascular events (heart surgery, catheterization, stent bypass, angioplasty, stroke, DVT)
• Previous breast cancer
• History of breast implants
• Breast reduction since last mammogram
• Mastectomy
• History of using Tamoxifen or Raloxifene
• Declined contact or use of data for research