Women using the the new aromatase inhibiting (AI) breast cancer drugs, anastrozole, letrozole and exemestane, should be aware of the risks of using vaginal estrogen, say researchers. The warning follows findings from a study published in the Annals of Oncology by a team from the Royal Marsden NHS Foundation Trust in London. AI drugs work by inhibiting the enzyme aromatase, which promotes the conversion of androgens to estrogens in postmenopausal women. Because breast cancer feeds off estrogen, reducing the circulating levels of the hormone as much as possible lessens the chance of the cancer recurring. The new AIs reduce circulating estradiol by as much as 97 percent. But around a fifth of patients on AIs suffer from atrophic vaginitis - a distressing skin condition of the genitals caused by a lack of estrogen. Patients often ask if they can use a topical estrogen, such as Vagifem, to alleviate the symptoms but the new study recommends against such a course of action. "Using this vaginal form of estrogen which, we found, increases systemic estradiol levels, will counteract AI treatment. With long term use, women may be risking the chance that their cancer may return," said researcher Ian Smith.
Vagifem is supposed to be used for a maximum of three months at a time, but the recurrence of symptoms often means repeat courses are prescribed. Vagifem's patient information sheet does state that Vagifem should not be used in women with a history of breast cancer, but it also states that although there are reports of increased risk of breast cancer in women on HRT, Vagifem is not expected to pose an increased risk.
"Our results raise concerns over the appropriateness of the combination of AI treatment and Vagifem, since the efficacy of aromatase inhibition depends on near total suppression of estrogenic stimulation. The third generation AIs that inhibit aromatase by over 97 percent are more effective in controlling breast cancer than earlier agents, which achieved only 90 percent; this suggests that even a small increase in systemic estrogen may be detrimental," said co-researcher Anne Kendall. Kendall added that women should consider non-hormonal vaginal moisturizing gels or creams that could be used as an alternative to estrogen preparations.
"It is important that women discuss this with their doctor. Some complications related to atrophic vaginitis, such as recurrent urinary tract infection, may need treatment to be completed before stopping Vagifem. One option in those cases would be to switch from AIs to tamoxifen, which appears not to allow as much estrogen to enter the system," Smith said in conclusion.
Source: European Society for Medical Oncology
