Decreasing rate of fatty involution at screening mammography.

Rationale And Objectives: This study was performed to document the perceived decrease in fatty involution at screening mammography during the past decade and evaluate the influence of hormone replacement therapy (HRT).

Materials And Methods: In December 1996, the mammograms of 261 consecutive screening patients with a comparison study obtained 5 years earlier were evaluated, and their breasts were categorized according to Breast Imaging Reporting and Data System categories for breast density. The women, aged 50-59 years, included 119 who had been receiving HRT for 0.25-15 years (mean, 3 years). From the files, 261 age-matched screening mammograms from 1986 were obtained; these patients also had comparison mammograms from 1981. Analysis of variance was used to determine differences between the 1980s group, the 1990s group receiving HRT, and the 1990s group not receiving HRT. Scheffé tests were used for post hoc comparisons. Stepwise regression analysis was used to evaluate the relative influence of age, decade, score of the first mammogram, and HRT.

Results: Breast density for the 1991 mammograms did not differ significantly from that in 1981 (P < .05). Initial breast density was the best predictor of final breast density in both decades (P < .001), regardless of HRT status. The change in breast density (toward fatty) over the 5-year interval in the 1980s (mean, 0.48) was significantly greater than that in both 1990s groups (mean for HRT group, 0.11; no HRT, 0.30; P < .05).

Conclusion: These results confirm that breast density at screening mammography in the 1990s did not decrease with age at the same rate as in the 1980s, even in patients not receiving HRT.