[Effect of hormone replacement therapy on the mammographic density of the female breast]

Mammographic parenchymal patterns are of particular interest because the denser patterns reduce sensitivity and they have been shown to be affected by exogenous oestrogens.

To evaluate the possible effects of peri- and postmenopausal hormone replacement therapy (HRT) on the mammographic density in the different types of parenchymal patterns.

During a period of 7 years (average: 3.44), 1158 women with combined or monophasic HRT were checked with mammography yearly. Their base-line mammograms were compared with those of 1433 screening participants of the same age (average 56 years). Mammograms were evaluated according to the Tabar classification. We studied the changes in density between two examinations in the HRT group, especially in the subgroup with benign lesion.

In comparison of the HRT and screening group, the distribution of their parenchymal patterns were similar. Pattern I (glandular) and II (adipose) eventually dominated, 38.9% and 47.9% in the HRT group, and 34.0% and 42.2% in the screening group. Pattern IV (adenotic) and V (fibrotic) types have been found in 8.9% of the HRT group, and 13.1% of the screening group. During HRT, an increase of breast density has developed after a few months, then it remained unchanged. Density increased in 30.8% of the whole HRT group, and in 38.0% of women who had benign lesions as well. Although there was a significant increase in breast density in case of pattern I-II and III (p=0.0013), pattern IV and V remained totally unchanged. The distribution of the patterns has changed significantly (p=0.0000) during HRT: the proportion of pattern I (glandular) type increased from 38.9% to 51.3%, pattern II (adipose) decreased from 47.9% to 30.6%, while the IV (adenotic) and V (fibrotic) types together showed no change.

Careful clinical and mammographic follow-up might be appropriate in women undergoing HRT, especially in those with benign lesion, because the HRT-induced increase in breast density proved significant.