By Karla Gale
WESTPORT, CT (Reuters Health) – Women who use hormone replacement therapy (HRT) are less likely to die from breast cancer than nonusers, according to the results of a meta-analysis conducted by researchers at the University of Maryland School of Medicine in Baltimore.
Dr. Jodi A. Flaws and colleagues searched the literature for peer-reviewed studies containing original data published between 1975 and 2000. They identified 45 papers that assessed the association between HRT and breast cancer risk.
"The relatively large body of literature on the association between estrogen and breast cancer is inconsistent," the authors write in Obstetrics and Gynecology for September. They add that "the distribution of risk estimates is what would be expected if there were no association." The investigators observed this pattern during the entire 25 years of research.
Eleven studies included analysis of mortality or survival related to breast cancer. Here, the data were more consistent and suggested a protective effect.
Dr. Flaws and her associates suggest that breast tumors that grow in the presence of estrogen are of lower grade, well differentiated, and slower to proliferate, which is analogous to what is observed for estrogen-associated endometrial tumors. The reduced risk of breast cancer mortality may also be related to the increased screening that hormone users undergo, which could lead to earlier diagnosis.
However, Dr. Eugenia Calle, director of analytic epidemiology at the American Cancer Society in Atlanta, disagrees with some of the conclusions drawn by Dr. Flaws' group. She referred to a 1997 Lancet report by the Collaborative Group on Hormonal factors in Breast Cancer as "truly unique and ground breaking" in that "it invited investigators from all over the world to resubmit their original data."
"It's like icing on the cake when it comes to meta-analyses," Dr. Calle told Reuters Health. This report "established a definite association" between HRT and recent and current use of HRT of long duration.
"I don't think that issue is open to debate anymore," she added.
Regarding the issue of mortality, Dr. Calle noted that such a collaborative group analysis has yet to be conducted. "I would say that the answer's not in yet. Most of a few studies have shown slightly better survival in women treated with HRT."
"Is it real? I don't know," she said. "It is an important question that remains to be resolved through further epidemiological study."