Background: Studies have suggested that mammographic density and pattern are affected by hormone replacement therapy (HRT) and may influence breast diagnosis. Because 40% of breast cancers diagnosed at our center are mammographically detected while still clinically occult, mammographic sensitivity is crucial. For this reason we studied the effect of HRT on mammographic density.
Methods: During a period of 18 months we studied consecutive women older than 54 years attending for breast screening. We recorded HRT use and dosing regimes. A breast density score (BDS) was developed and applied to all mammograms.
Results: Mammograms of 148 HRT users were compared with those of 158 nonusers. HRT users had a significantly higher mean density score (4.7 versus 3.4; p < 0.001). Only 11% of non-HRT users had high scores compared with 37% among HRT users (p < 0.001). The significant difference remained when women were stratified by age. Duration of HRT (longer or shorter than 5 years) did not affect density scores.
Conclusions: HRT is associated with a significant increase in breast density. In turn, density and mammographic sensitivity are related. The possibility that increased breast density will hamper mammographic diagnosis of clinically occult cancers is worrisome.