CA: A Cancer Journal for Clinicians, Vol 40, Issue 5 289-296, Copyright © 1990 by American Cancer Society
Hormone-replacement therapy and the risk of breast cancer
B. S. Hulka
Department of Epidemiology, University of North Carolina, Chapel Hill.
At least 30 epidemiologic studies designed to identify an association
between hormone-replacement therapy and breast cancer risk have been
published since 1974. In general, the design, quality, and analytic
strategies used in these studies have improved over the years, and the
number of subjects in each study has increased. The results from studies
published prior to 1985 can be summarized as showing a small increase in
the risk of breast cancer after many years of estrogen use. Even this
tentative conclusion is debatable, however, since many rigorous studies
showed no association between estrogen use and breast cancer. This review
will summarize the earlier findings and emphasize several large, recent
studies that add at least two new dimensions to this body of research; they
provide data from Europe and on the addition of progestins to the
therapeutic regimen. This review indicates the following: 1. Analyses of
ever versus never use of estrogen-replacement therapy show no association
with breast cancer risk. 2. Duration of estrogen-replacement therapy
affects risk. Based on studies in the United States, a relative risk of
about 1.5 may be reached after 15 or more years of use. 3. The increase in
risk after long-duration hormone use is present for women with either a
natural or a surgical menopause. 4. European studies exhibit higher risks
after shorter durations of hormone use than do US studies. 5. The type of
estrogen used and the addition of progestins to hormone-replacement therapy
may alter the risk of breast cancer. Data that substantiate these points
are reviewed and placed in context with hormonal theories of
carcinogenesis.
