Background: It has been known for some time that oral contraceptives substantially reduce the risk of endometrial and ovarian cancer, but they do not reduce the risk of breast cancer. A hormonal contraceptive regimen has been developed which uses a gonadotropin-releasing hormone against (GnRHA) to suppress ovarian function, and this regimen includes the administration of very low doses of both estrogen and progestogen. This hormonal contraceptive regimen attempts to minimize exposure of the breast epithelium to these steroids and to preserve the maximum beneficial effects of estrogen, while still preventing endometrial hyperplasia.
Purpose: Our purpose was to determine whether changes occurred in mammographic densities between baseline and 1 year for women on this hormonal contraceptive regimen with reduced estrogen and progestogen levels compared with women in a control group.
Methods: Twenty-one women were randomly assigned in a 2:1 ratio to the GnRHA-based contraceptive group (14 women) or to a control group (seven women). The contraceptive group received the following: 7.5 mg leuprolide acetate depot by intramuscular injection every 28 days; 0.625 mg conjugated estrogen by mouth for 6 days out of 7 every week; and 10 mg medroxyprogesterone acetate orally for 13 days every fourth 28-day cycle. The control group received no medication. Baseline and 1-year follow-up mammograms of contraceptive and control subjects were reviewed in a blinded fashion by two radiologists.
Results: Comparison of the changes between the baseline and 1-year mammograms in the two groups of women showed significant (P = .039) reduction in mammographic densities at 1 year for women on the contraceptive regimen. Assessing the reduction in mammographic densities by noting the fineness of fibrous septae showed a highly significant (P = .0048) difference in the contraceptive regimen group. One of the women on the contraceptive regimen was withdrawn from the study because of poor compliance.
Conclusion: The reduced estrogen and progestogen exposures to the breast that were achieved by the hormonal contraceptive regimen resulted in substantial reductions in follow-up mammographic densities at 1 year compared with baseline. Although there is no direct evidence that such a reduction in densities will lead to a reduced risk of breast cancer, indirect evidence for a protective effect of this regimen is that early menopause reduces breast cancer risk, and that menopause is associated with a reduction in mammographic densities.
PIP: In California, physicians randomly assigned 21 women aged 25-40 to either the contraceptive group or the control group as part of a study aimed to determine whether or not a hormonal contraceptive regimen with reduced estrogen and progestogen levels affects mammographic densities. Eligibility criteria included premenopausal women with a 5-fold greater than normal risk of breast cancer, no prior cancer, bone mineral density not less than 2 standard deviations below normal, normal cholesterol, and a normal physical and pelvic examination. The contraceptive group received intramuscular injection of 7.5 mg leuprolide acetate depot every 28 days, 0.625 mg oral conjugated estrogen for 6 out of 7 days every week, and 10 mg oral medroxyprogesterone acetate for 13 days every fourth 28-day cycle. The reduction in mammographic densities in women on the contraceptive regimen between baseline and 1 year was significantly different than that of the controls whose mammographic densities remained essentially the same (p = 0.039). Cases had significantly more change in fibrous septae between baseline and 1 year than did controls (+0.82 units vs. -0.07; p = 0.0048). These results indicate that lower levels of estrogen and progestogen reduces mammographic densities, which may reduce the risk of breast cancer since increased mammographic densities are linked to an increased risk of breast cancer. Reduced mitotic activity in breast epithelial cells during menopause and with lower levels of estrogen and progestogen (i.e., reduced mammographic densities) suggest that early menopause may also protect against breast cancer.