Although several large studies in recent years have linked the use of hormone therapy after menopause with an increased risk of breast cancer, the authors of a new analysis claim the evidence is too limited to confirm the connection.
Together, the results of these studies found overall an increased risk of breast cancer among women who used the combination form of hormone therapy with both estrogen and progesterone. Women who have had a hysterectomy and use estrogen-only therapy also have an increased risk, two of the studies found. The WHI, however, found that estrogen-only therapy may not increase breast cancer risk and may actually decrease it, although that has not been confirmed in other research.
After the WHI study was published in July 2002, women dropped hormone therapy in droves. Many experts pointed to that decline in hormone therapy use as the reason breast cancer rates were declining.
Not so, Shapiro said: "The decline in breast cancer incidence started three years before the fall in HRT use commenced, lasted for only one year after the HRT drop commenced, and then stopped."
For instance, he said, between 2002 and 2003, when large numbers of women were still using hormone therapy, the number of new breast cancer cases fell by nearly 7 percent.
In taking a look at the three studies again, Shapiro and his team reviewed whether the evidence satisfied criteria important to researchers, such as the strength of an association, taking into account other factors that could influence risk. Their conclusion: The evidence is not strong enough to say definitively that hormone therapy causes breast cancer.
The study is published in the current issue of the Journal of Family Planning and Reproductive Health Care.
The new conclusion drew mixed reactions from experts.
In an editorial accompanying the study, Nick Panay, a consultant gynecologist at the Queen Charlotte's & Chelsea Hospital in London, supported the conclusions of the new analysis. "If there is a risk, the risk is small, and the benefits of HRT can be life-altering," he wrote. "It is vital that we keep this in perspective when counseling our patients."
The hormone therapy in use today, Panay said, is lower in dose than those used in the previous research. "In principle, we tend to start with lower doses than we used to and increase as required until full symptom relief has been achieved," he said.
What is needed now, he said, is a clinical trial in which the hormone therapy in use today is compared with placebo, to evaluate the risks and benefits.
Another expert took a more middle-of-the-road view about the potential link.
"It would be hard to say the entire decline [in breast cancer rates] is due to the decline in HRT use," said Dr. Steven Narod, the Canada Research Chair in Breast Cancer at the University of Toronto.
According to Dr. Susan Gapstur, vice president of epidemiology for the American Cancer Society, the new analysis overlooks some other important information. "Indeed, there is a much larger body of scientific evidence from clinical trials and from observational epidemiologic studies comparing breast cancer incidence rates in women who used HRT to those who did not that demonstrate the risks and benefits of HRT for chronic diseases," she said.
"Women need to discuss with their doctors the risk and benefits of taking HRT for the primary prevention of chronic disease, including breast cancer," she added.
Narod said hormone replacement is an excellent therapy for some women. Therapy that includes progesterone carries more risk, he said, and limiting use to five years or less seems wise.
Shapiro has performed consulting work for the manufacturers of hormone therapy, and Panay has received grants from pharmaceutical companies.