Executive Summary

ESTROGEN REPLACEMENT THERAPY: BREAST CANCER RISK IS "NOT CONCLUSIVE," the Fertility and Maternal Health Drugs Advisory Committee determined at a Feb. 1 meeting. "While the evidence is not conclusive, some studies have reported increased risk of breast cancers in long term users of estrogen replacement therapy. Other studies have not shown this relationship," the panel unanimously agreed. The committee added that it did not have adequate data to distinguish the relative effects of different types of estrogen. A review of the available data led the committee to conclude it "does not believe that there is sufficient data about the effect of progestins added to estrogen replacement therapy on the risk of breast cancer." However, the committee "felt that the addition of progestins to estrogen replacement therapy decreases the risk of endometrial cancer." The panel voted 8-1 with one abstention that it is ethical to conduct clinical trials of hormone replacement therapy which include estrogen-only groups as long as they are short term, carefully designed and well monitored. The committee addressed concerns sparked by recent studies about the risk of breast and endometrial cancer associated with hormone replacement therapy. The objective of the meeting was to offer FDA guidance on the current status of research on that topic. A second meeting, scheduled for June 14-15, will address the potential cardiovascular effects of hormone replacement therapy. A key issue will be to determine if the cardioprotective effect associated with estrogen is affected by the addition of progestin. The final goal of the two meetings is to define a hormone replacement regimen that will balance the risks and benefits of such therapy. A recent study by Bergkvist, et al., evaluating cancer risks of hormone replacement therapy was of particular concern to the committee. The Swedish study, published in the Aug. 3 issue of The New England Journal of Medicine, reported an increased risk (relative risk of 1.7) of breast cancer in women who had taken estrogen for a period of over nine years. The investigators performed a prospective study of 23,244 Swedish women 35 years of age or older who had filled at least one prescription for estrogen replacement therapy. A follow-up study was conducted with 253 women who had subsequently developed breast cancer. The investigators also reported a four-fold increased risk of developing breast cancer in women who took a combination of estrogen and progestin for more than six years. Commenting on that finding, National Cancer Institute Environmental Epidemiology Branch Chief Robert Hoover, MD, who participated in analyzing the data for publication, said at the meeting: "While the risk was 4.4, that doesn't necessarily mean that the combined regimen was worse than estrogen alone. All it means is we failed to see a reduction in excess risk." He also noted that the figure was based on only 10 cases. Labeling for several hormone replacement therapies already includes some precautions and warnings on cancer risks. For example, the precautions section of Wyeth-Ayerst's Premarin, the most widely used estrogen replacement product, advocates the use of progestins to curb the possible risk of endometrial cancer: "Studies of the addition of a progestin for seven or more days of a cycle of estrogen administration have reported a lowered incidence of endometrial hyperplasia...Whether this will provide protection from endometrial carcinoma has not been clearly established." Regarding breast cancer, the Premarin patient information leaflet states: "The majority of studies have shown no association with the usual doses used for estrogen replacement therapy and breast cancer. Some studies have suggested a possible increased incidence of breast cancer in those women taking estrogens for prolonged periods of time and especially if higher doses are used."