WEDNESDAY, April 6, 2005 (HealthDay News) -- High doses of progestin in hormone replacement therapy may explain the regimen's link to breast cancer recurrence in women with a history of the disease, a new study finds.
While hormone therapy is not typically recommended for women who have had breast cancer, Swedish researchers reporting in the April 6 issue of the Journal of the National Cancer Institute say they launched the study to assess the effect of hormone replacement therapy (HRT) after a diagnosis of breast cancer.
Their findings suggests that HRT with minimal or no progestin is much safer.
The new study won't change prescribing practices overnight, "but it will likely change the way physicians look at this question," said Dr. Rowan T. Chlebowski, a medical oncologist at the Los Angeles Biomedical Research Institute at Harbor/UCLA Medical Center, who co-authored an editorial accompanying the study.
The finding is also apt to spark more research into the issue, he added.
HRT's reputation as a safe method of easing menopausal symptoms has never recovered from the 2002 findings of a large, ongoing study known as the Women's Health Initiative. In that trial, early results indicated the regimen increased women's risks for heart attack, stroke, blood clots and breast cancer. Use of HRT among American women soon fell dramatically.
In this latest study -- focused on women with a prior history of breast cancer -- researchers at the Karolinska Institute, in Stockholm, tracked breast cancer recurrence in 378 breast cancer patients randomly assigned to receive either hormone replacement therapy or no treatment for five years. Nearly three-quarters (73 percent) of the women were assigned to hormone therapy received either estrogen alone or a regimen in which lower than usual levels of progestin were given.
The researchers say they found no association between hormone therapy use and the risk of breast cancer recurrence after 4.1 years of follow-up. Specifically, 11 of the 188 women assigned to the hormone group experienced a recurrence of breast cancer, compared to 13 of the 190 women assigned to the group with no hormone therapy.
The results differ from those of a similar trial -- known as the Hormonal Replacement Therapy Is It Safe? (HABITS) -- in which 434 breast cancer patients were assigned to receive either hormone therapy or no treatment. When the risk of breast cancer recurrence was found to be 3.3 times higher among the hormone-taking group, the HABITS trial was stopped early in December 2003. The Stockholm trial was closed prematurely for patient entry at the same time.
However, the low/no-progestin hormone regimen used in the Stockholm trial may explain the differences in results between the two studies, the Swedish team said.
"Our hypothesis when starting the study was that there would not be an increased risk for recurrence,'" said Eva von Schoultz, a researcher at Karolinska University Hospital & Institute and a member of the Stockholm Breast Cancer Study Group. "So we were not surprised."
Of the HRT-breast cancer link, she said, "We and others think the combination of progestin and estrogen is to blame."
The differences in results from the two studies may be also partly due to the conditions of the patients, or to study design, von Schoultz wrote.
Evidence has begun to accumulate that the combination treatment may carry a greater risk for breast cancer than estrogen by itself, von Schoultz noted.
About 211,000 women in the United States will be diagnosed with invasive breast cancer in 2005, according to American Cancer Society estimates, while about 40,000 die from the disease annually.
Putting the host of studies in perspective, Chlebowski said that the HABITS study results, released earlier, "reinforced the feeling there is a great reluctance" to use HRT in breast cancer patients due to risk of recurrence.
"Now the question is a little different--what is the real role of estrogen-only in breast cancer growth?''
Eventually, he said, "it might be possible to come up with a regimen that would be safe for those with breast cancer."
Evidence is accumulating, he wrote, that "progestin use is associated with an increased breast cancer risk, compared with its nonuse." For now, however, he wrote, non-hormone-based treatments for menopausal symptoms in breast cancer survivors are preferred in most circumstances.
"The message for women with breast cancer is that this study was prematurely closed," von Schoultz said. Therefore, at this point in time, " we cannot support the use of hormone therapy after a breast cancer diagnosis. More studies must be done."
To learn more about breast cancer, visit the American Cancer Society.