Experts have moved to reassure former breast cancer patients taking HRT, after researchers said it could raise the risks of a new tumour.
There are fears over the return of cancer
A Swedish study of breast cancer survivors was halted early after cancer came back more often in HRT users.
However, consultants treating women for severe menopausal problems said that other, unpublished, research had found no evidence of an extra risk.
The study, in The Lancet, comes after two others raising HRT safety fears.
Women in general have been urged to limit the duration of time they take HRT in the wake of studies suggesting a doubling of the risk of breast cancer.
However, the overall risk of cancer remains small, and HRT is still recommended by experts for those whose quality of life is hit by menopausal problems such as hot flushes and night sweats.
Drug manufacturers themselves advise not giving HRT to anyone with a history of breast cancer - although doctors are not strictly bound by this guidance.
Thousands of cases
Thousands of pre-menopausal women in the UK are diagnosed with breast cancer each year. Two-thirds of those who survive will develop menopausal symptoms, either naturally or as a result of their treatment regime.
Many experts still feel that for women with the most severe symptoms, even those who have been treated for cancer, HRT remains an option, provided information about cancer risk is explained properly to the patient before a prescription is written.
The therapy can be given in conjunction with the drug tamoxifen as an additional safeguard against the return of the cancer.
The latest study looked at the effects of hormone replacement in more than 170 female breast cancer survivors.
It was due to continue for several more years, but after a fraction of that, the Swedish doctors running it decided the evidence that HRT was a danger to breast cancer patients meant they had to halt it.
HRT has major benefits as well as some risks
Of the 174 women on HRT, breast cancer came back in 26 cases, compared with just seven in a similarly sized group - apparently a clear-cut warning against the treatment.
The study authors described this as an "unacceptable risk" to women exposed to HRT.
However, a similar trial running alongside this one produced a completely different picture, suggesting no increase in risk for women in the same circumstances.
Dr Richard Sullivan, from Cancer Research UK, said that this left a far from clear picture for both doctors and their patients.
He said: "The downside is that women who develop breast cancer early in their lives will be left wondering whether or not it is safe to take HRT - a question which is now unlikely ever to be definitively answered."
Studies on hold
Similar studies hoping to probe the issue have also been put on hold in the wake of the Swedish results, including one at London's Royal Marsden Hospital.
Mr Nigel Sacks, leading the Marsden study, told BBC News Online that he was pessimistic about the chances of it being completed in the wake of the Swedish research.
However, menopause experts said that there remained definite circumstances in which it would be justified to prescribe HRT to breast cancer survivors.
Dr John Stevenson, from the Royal Brompton Hospital in London, and a past chairman of the British Menopause Society, said: "We have some patients whose symptoms are so severe that their quality of life is very low.
"We explain the possibility that HRT may increase their risk of breast cancer recurrence, and they choose HRT."
He said: "Provided the patient makes an informed choice, that is right for them."
A spokesman for the Department of Health said that the general advice was for women with a history of breast cancer to avoid HRT - and had been for some years.
She added: "This study backs up what is already suspected about the risks of HRT for women with a history of breast cancer."
Official advice on the wider use of HRT suggests that women should take it only when absolutely necessary and for the shortest possible duration.
The "Million Women Study", published in August, pointed to a doubling of the risk of breast cancer among patients taking HRT for several years.
Combination HRT, which includes the hormone progestogen, caused the biggest increase in risk, although the overall threat remains relatively small.
I stopped taking the combination HRT Premique after 10 years. All symptoms returned within three months. I visited my doctor who suggested that I should remain on the HRT for another couple of years. The symptoms had gone within 3 days of resuming taking HRT. I also tried to gradually stop by taking it every other day. This also caused the symptoms to return. I am worried about the reports regarding the risk of breast cancer, but my quality of life is very much affected by not taking HRT.
Gillian Padgham, Suffolk
I had both ovaries removed last year during a hysterectomy. I was thrown immediately into brutal menopause. The doctors said I had to take HRT. I declined. It was bad at first but I survived, my body has adjusted naturally and I hardly ever have hot flashes now.
Lisa, Halifax, Nova Scotia, Canada
Don't think of them as hot flashes but as a warm glow! Think of time quietly to read instead of insomnia! Think of taking care of your life instead of HRT. There are alternatives. Ask questions, read literature, browse the internet and make your own decisions.
Jan Cordani, Maryland, USA
My mother who is 61 took HRT for about 11 years then developed breast cancer last May. After removal of the lump she is now alright. I still say it was HRT which caused this. I am 44 and no matter what I will not be taking HRT. Why do doctors dish it out willy nilly? More research needs to be done on this subject and the public made aware of the consequences of taking HRT.
Beverley Sampat, Uxbridge
After the latest research my doctor advised coming off HRT. This opinion was repeated by 2 further doctors, as I had been on HRT for more than 10 years. I have no family history of breast cancer, but with this advice I chose to stop taking the drug in September. The last months have been "interesting". Hot flushes and night sweats have been troublesome and I also wonder if some of my feelings would be like a drug addict trying to kick the habit.
Pat Thompson, Bordan, Hampshire, England
When I was suffering menopause symptoms a friend suggested I read Passage to Power written by Leslie Kenton. I would recommend it to all women. Following the excellent advice I bought wild yam capsules from the health food shop and within 24 hours the flushes were under control.
Denise Edwards, Devon UK
I've been taking HRT for 4 years now. Once the dose was stabilised, I've had no problems with hot flushes or night sweats. I had a mammogram last year which was clear. My skin is still young and I feel fit. I've been on the Pill in total for around 30 years with no problems and can recommend it wholeheartedly.
Julia Newton, Zurich, Switzerland
I stopped taking HRT and now take Fosamax to strengthen my bones. The downside is that the hot flushes have returned, concentration levels plummeted and I'm not sleeping so well! Even so, I am not keen to return to taking HRT due to the issues raised about breast cancer.
Felicity Hector, Leicester