Breast cancer specialists cautioned doctors of the risks in prescribing vaginal oestrogen to breast cancer patients being treated with the new aromatase inhibiting drugs, Anastrozole ( Arimidex ), Letrozole ( Femara ) and Exemestane ( Aromasin ).

Their concerns follow findings from the first study to examine the impact of vaginal oestrogen in women receiving aromatase inhibitors ( Ais ) for breast cancer, published in the Annals of Oncology, by a team from the Royal Marsden NHS Foundation Trust in London.

Aromatase inhibitors work by inhibiting the enzyme aromatase, which promotes the conversion of androgens to oestrogens in postmenopausal women. Breast cancer feeds off oestrogen, so reducing the circulating levels of the hormone as much as possible lessens the chance of the cancer recurring. The new aromatase inhibitors reduce circulating oestradiol by over 97%.

Around a fifth of patients on adjuvant aromatase inhibitors suffer from atrophic vaginitis, a distressing skin condition of the genitals caused by lack of oestrogen.
Many ask if they can use topical oestrogen to alleviate the symptoms as conventional HRT is not recommended.

Senior author Ian Smith, Head of the Breast Unit at the Royal Marsden, said: " Using this vaginal form of oestrogen which, we found, increases systemic oestradiol levels, will counteract aromatase inhibitor treatment. With long term use, women may be risking the chance that their cancer may return, although this is probably not an issue if oestrogen rises for only one to two months."

Using a sensitive radioimmunoassay, the researchers measured serum oestradiol in six women on adjuvant aromatase inhibitor therapy who had actively asked to use the vaginal oestradiol tablet Vagifem for severe symptoms of atrophic vaginitis.
They also monitored a seventh patient with metastatic breast cancer who was using Premarin oestradiol cream. Measurements were taken at baseline, then at 2, 4, 7-10 weeks and over 12 weeks from starting Vagifem.

Lead eesearcher Anne Kendall, at the Royal Marsden, said: " Our results showed a significant rise in serum oestradiol levels two weeks after starting Vagifem in six of the seven women ( five of those on Vagifem and the one on Premarin ). Typically, they fell after one month, but with a return to pre-Vagifem levels in only two women after seven and 12 weeks respectively. Two women who continued using Vagifem showed further increases between weeks seven and 10.”

Although Vagifem is supposed to be used for a maximum of three months at a time, recurrence of symptoms often means repeat courses are prescribed. The 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.

Smith said: " Although the study is small, the magnitude of the effect in such a high proportion of the women strongly indicates it would be reproduced in a larger study population. It is particularly important that doctors are aware of the new findings, as increasing uptake of aromatase inhibitor therapy means that it is likely that around 15,000 new women a year in the UK would be receiving aromatase inhibitors, a total of 100,000 at any one time."

The women in the study had been warned at the outset that they would be recommended to stop using the topical preparation at an early stage if there were concerns. One patient continued to use a low dose with regular monitoring. One elected to stop aromatase inhibitor treatment and continue with Vagifem because of her poor quality of life. The others have stopped.

Kendall said: " Our results raise concerns over the appropriateness of the combination of aromatase inhibitor treatment and Vagifem, since the efficacy of aromatase inhibition depends on near total suppression of oestrogenic stimulation. The third generation aromatase inhibitors that inhibit aromatase by over 97% are more effective in controlling breast cancer than earlier agents, which achieved only 90%; this suggests that even a small increase in systemic oestrogen may be detrimental."

She added: " Our view is that the combination of aromatase inhibitors and Vagifem is contraindicated, apart from exceptional circumstances where regular monitoring of plasma oestradiol with specialist assays is available. Other non-hormonal vaginal moisturising gels or creams should be used in most cases." She said it was impossible to generalise about all vaginal oestrogens. However, given that a similar effect was seen with Premarin cream, caution was needed with all topical oestrogens.

Source: European Society for Medical Oncology, 2006


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