In women with a history of breast cancer, using hormone replacement therapy (HRT) did not increase the risk of breast cancer recurrence or death.
The findings add to a growing body of research examining the effects of HRT on cancer risk.
Due to declining oestrogen levels, menopause can cause vaginal dryness, hot flashes, sleep disruption and other symptoms. HRT is one of the most effective ways to relieve these effects. It works by raising oestrogen levels either throughout the body, in what’s called systemic oestrogen therapy, or near the vagina, with vaginal oestrogen therapy.
But the safety of HRT has been hotly debated.
Most breast cancers rely on the hormone oestrogen to grow, says Debasish Tripathy at the University of Texas MD Anderson Cancer Center in Houston. As such, many breast cancer therapies work by reducing or halting oestrogen production, which can lead to menopause-like symptoms.
The concern, then, is that increasing oestrogen levels to alleviate these symptoms could increase breast cancer risk, especially in people with a personal or family history of the disease.
Several studies have found that HRT is associated with an increased risk of breast cancer, though last year an analysis of 300,000 women found that taking HRT to alleviate menopause symptoms does not increase the risk of dying early. Past research has also found that, in people who have had breast cancer, HRT can increase the risk of recurrence.
To further investigate the risk of recurrence, Søren Cold at Odense University Hospital in Denmark and his colleagues collected data on 8461 post-menopausal women in Denmark who had been diagnosed with early-stage breast cancer between 1997 and 2004 and received treatment. Of these, 1957 then used vaginal oestrogen therapy and 133 used systemic hormone therapy either alone or with vaginal oestrogen therapy. Before cancer treatment none had used HRT.
After 10 years, 15.4 per cent of those using vaginal oestrogen therapy and 17.1 per cent of those using systemic hormone therapy had their cancer recur compared with 19.2 per cent of those not using either treatment. There was no association between HRT use and death.
Women who used vaginal oestrogen therapy together with a class of drugs called aromatase inhibitors, which stop oestrogen production, were more likely to experience a recurrence, but had no higher risk of premature death. There was no increased risk of recurrence in women who used vaginal oestrogen therapy alongside the drug tamoxifen, which selectively blocks oestrogen in breast cells.
“I think the reason we’re seeing a worse effect with aromatase inhibitors is that by replacing oestrogen, you’re directly counteracting how aromatase inhibitors work,” says Tripathy, who wasn’t involved in this research.
“I don’t think [these results are] conclusive enough to tell someone that they can safely use these oestrogen products,” says Tripathy, pointing out that the study size was quite small, especially for those using systemic hormone therapy. But for people who have had breast cancer, he says that “if you absolutely have to use oestrogen replacement you should probably be on tamoxifen as opposed to an aromatase inhibitor.”
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