A re-evaluation of the Women’s Health Initiative demonstrated that women taking cHRT showed a greater increase in mammographic breast density and a greater increase in breast cancer risk than what was previously calculated.

BACKGROUND: It has been shown in previous clinical trials that estrogen plus progestin users had a 24% increased incidence of breast cancer compared to participants assigned the placebo, this led to a decline in estrogen plus progestin use. There have also been observational studies confirmed by clinical trials that report an increase in mammographic breast density with estrogen and progestin use. Numerous studies have also indicated that “mammographic density strongly predicted breast cancer risk.”

The aim of this study was to determine the extent that mammographic density changes following estrogen plus progestin use and how that relates to increased breast cancer incidence.

METHOD: The study was conducted within the Women’s Health Initiative, where postmenopausal women were randomly assigned to either daily estrogen plus progestin therapy or placebo for one year. Mammograms were performed prior to commencement of therapy and then again after one year to assess mammographic breast density.

RESULTS: The mean change seen in women taking the placebo was a decrease in mammographic density by 0.05% after one year. Noticeably, the mean change seen in women on estrogen plus progestin was an increase in mammographic density by 9.73% after one year.

“Baseline mammographic density did not increase breast cancer risk among women assigned placebos, but breast cancer risk increased 3% among women assigned estrogen plus progestin.”

CONCLUSION: “We found the one-year change in mammographic density after estrogen plus progestin initiation predicted subsequent increase in breast cancer risk. All of the increased risk from estrogen plus progestin use was mediated through mammographic density change.”