Objective: The prolonged use of estrogen therapy is associated with a
slightly increased risk of breast cancer. Alternative therapies that are
effective in the prevention of menopause, having associated morbidities
but no unwanted effects, are of primary interest in the pharmacologic
research. The aim of this study was to evaluate the effect of two
alternative to estrogens drugs, the selective estrogen receptor
modulator raloxifene and the tissue-specific tibolone, on the
mammographic appearance of the breast.
Design: The study group comprised 131 postmenopausal women aged 41 to 67
years. The women were at least 2 years postmenopausal, free of
climacteric symptoms, and at the time of entry to the study had not had
therapy for at least 9 months. Women with risk factors for osteoporosis
or cardiovascular disease were allocated either to tibolone (n = 56) or
raloxifene (12 = 48) therapy. Women with no risk factors and women who
either did not qualify for or denied treatment (17 = 27) served as
controls. The study duration was 12 months. Women received a baseline
mammogram before commencing therapy and a repeat mammogram at the end of
the study period. Mammogram findings were classified according to the
modified Wolfe criteria by two expert radiologists.
Results: No difference was identified between groups with respect to
baseline characteristics associated with breast cancer risk. Similarly,
no difference was detected between groups concerning the modified Wolfe
classification of baseline mammographic findings. In the tibolone group,
10.7% of the women showed an increase in breast density in the 12-month
reevaluation. The respective figure in the raloxifene group was 6.3%,
whereas no woman in the control group showed an increase in breast
density. Differences in the increase in breast density between groups
did not, however, reach statistical significance. Accordingly, 10.7% of
women in the tibolone group and 18.8% of women in the raloxifene group
exhibited involutionary changes in the repeat mammogram, whereas 25.9%
of women in the control group revealed a decrease in breast density in
the 12-month examination. The percentages were not significantly
different between groups.
Conclusions: Breast density as shown by mammography was stable in a
majority of patients and changed in a minority of cases for both
tibolone and raloxifene. In most patients, these drugs are not likely to
interfere with mammogram interpretation. Larger long-term studies are
needed to confirm the impact of prolonged tibolone or raloxifene
administration on mammography