A new report adds weight to the idea that recurring breast cancer (search) may be related to which hormones are used in therapy for women after menopause.
One trial, called HABITS, was halted in 2003, after women receiving the hormones estrogen and progestogen showed an increased risk of breast cancer recurring, compared to women not receiving hormones.
But a second study, the Stockholm trial, using a different therapy concentrating on estrogen, had no increase in breast cancers, according to a paper appearing in Wednesday's issue of the Journal of the National Cancer Institute.
Both studies, done in Sweden, were intended to test the effects of hormone replacement therapy for post-menopausal women who had been diagnosed with early-stage breast cancer.
Many women stopped using hormone replacement therapy after a 2002 study indicated they faced an increased risk of heart disease and strokes. After suffering severe symptoms, some have returned to hormone therapy, however, and medical authorities currently recommend that those women who need therapy use the smallest estrogen dose possible.
"Although it is tempting to speculate that treatment regimens with estrogen and a minimum of progestogen (also known as progestin) may be safe, the management of menopausal symptoms and quality of life for patients with breast cancer remains an important unsolved problem," the authors of the new paper said in a statement.
"Because doses of estrogen and progestogen and treatment regimens may be associated with the recurrence of breast cancer, there is an urgent need to identify safe and effective strategies to manage menopausal symptoms and improve the quality of life for patients with breast cancer," wrote Dr. Eva von Schoultz and Dr. Lars E. Rutqvist of the Karolinska Institute, in Stockholm, Sweden.
There were other differences in the two studies that could also have had an effect, they reported. For instance, more women in the Stockholm trial had received tamoxifen for their cancer than in the HABITS trial, and the timing of the hormone therapy differed between the two groups.
The need for further study also was stressed in an accompanying editorial in the journal by Dr. Rowan T. Chlebowski of the Los Angeles Biomedical Research Institute and Garnet L. Anderson of the Fred Hutchinson Cancer Research Center in Seattle.
They noted that while the results offer evidence that use of combined estrogen and progestin was associated with an increased risk of breast cancer, more research is needed on the effects of estrogen alone.
The study was funded by the Stockholm Cancer Society, King Gustav V Jubilee Fund, the Swedish Research Council and Karolinska Institute.