THURSDAY, Jan. 26, 2006 (HealthDay News) -- Estrogen used to combat vaginal dryness and other postmenopausal symptoms may counteract the beneficial effects of new breast cancer drugs called aromatase inhibitors, a new British study finds.
Although the study involved only a small number of women, its authors believe the findings warrant possible treatment changes.
"Women on aromatase inhibitors using this and similar preparations should discuss their situation with their doctor," advised Dr. Anne Kendall, lead author of the study and a clinical research fellow in the breast and biochemistry unit at Royal Marsden Hospital in London. "In the majority of women, we would anticipate that they would stop the vaginal estrogen therapy."
Other experts, however, do not agree with that prescription.
"It's an interesting observation but it's a small study and it needs further research," said Dr. Jay Brooks, chairman of hematology/oncology at the Ochsner Clinic Foundation in Baton Rouge, La. "I would not alter the way I prescribe medication."
The findings appear in the Jan. 26 issue of Annals of Oncology.
Aromatase inhibitors (AIs) such as anastrozole, letrozole and exemestane are increasingly being used for breast cancer treatment in postmenopausal women. The drugs work by inhibiting the aromatase enzyme which, in turn, limits the production of estrogen. Estrogen fuels the growth of many breast cancers.
According to the study, many postmenopausal women, including about one-fifth of patients taking aromatase inhibitors, also suffer from atrophic vaginitis. This condition, caused by a lack of estrogen, can involve dryness, pain and urinary incontinence. Aromatase inhibitors, which can reduce circulating estradiol (the major estrogen) by more than 97 percent, can worsen these symptoms.
"With the increasing number of women using adjuvant aromatase inhibitors, we have become aware of more women reporting such side effects in our clinics," Kendall said. "Pragmatically, many of these women have been offered vaginal estrogen therapy as it is perceived to have a low systemic absorption of estrogen. We were keen to clarify the safety of this approach, particularly using our sensitive assay that can measure the low levels of estrogen seen in these women."
Kendall and her colleagues measured blood levels of estradiol in six women. All six women were also on adjuvant aromatase inhibitor therapy and were using Vagifem -- estradiol tablets for severe symptoms of atrophic vaginitis.
A seventh patient with metastatic breast cancer was also included in the study. This woman was using a different but similar product, Premarin estradiol cream. All women had estradiol levels measured at regular intervals up to 12 weeks after starting vaginal estradiol.
Five of the women on Vagifem and the woman on Premarin experienced a significant increase in estrogen levels two weeks after starting the product. Levels fell after one month but only returned to pre-Vagifem levels in two women (after seven and 12 weeks). Two other women showed additional increases between weeks seven and 10.
The authors acknowledged that the study sample was small but felt that the magnitude of the effect raised a red flag, especially given the increasing numbers of women using aromatase inhibitors.
The efficacy of AIs depends on "near total suppression of estrogenic stimulation," they wrote.
Package insert material for Vagifem indicates that the product may increase breast cancer risk and states that it should not be used in women with a history of breast cancer. It does not, however, address the issue of taking it as a breast cancer patient.
Kendall suggested that women who have atrophic vaginitis may wish to switch from aromatase inhibitors to another breast cancer-supressing drug, tamoxifen, for two to three months, enough time to improve their symptoms before switching back to AIs. Non-hormonal preparations could also be considered, she said.
More information
For more on aromatase inhibitors, head to the National Cancer Institute.
