A study has found hormone replacement therapy can increase the risk of developing breast cancer in women with a history of the disease.
Women on HRT are advised to talk to their doctor
But other experts say unpublished research suggests there is no extra risk.
BBC News Online looks at the confusion over HRT.
Q: What did this study look at?
The Swedish study looked at women who had already had breast cancer, some of whom were taking HRT.
Of 174 women on the drug, breast cancer returned in 26 cases, compared to just seven in a similarly sized group who were not taking HRT.
After researchers saw the results, they halted the trial three years early because they believed the risks to women outweighed the benefits.
Have other studies raised worries?
Some have. A study of a million women, published last year, suggested taking the combined oestrogen and progestogen HRT for several years doubled a woman's risk of developing breast cancer.
Another US study was stopped early in 2002 after indications HRT use could increase a woman's risk of breast cancer and heart disease.
But others have suggested there is no increased risk.
An unpublished study running alongside the Swedish trial, has shown no increased risk of recurrent breast cancer in women taking HRT.
Are there any benefits in taking HRT?
Women take the medication for the relief of menopausal symptoms, such as hot sweats.
At the menopause, levels of the sex hormone oestrogen decline, causing symptoms such as hot flushes and contributing to the serious brittle bone disease osteoporosis. HRT can reverse this.
In the Million Women study, experts said short-term HRT can be beneficial.
Women at risk of developing osteoporosis can benefit from taking HRT - though doctors say other treatments and lifestyle changes can reduce women's risk.
I'm taking HRT. Should I stop?
No. But women are advised to discuss their concerns with their doctor.
Experts say each woman has to decide whether, for her, the benefits of taking HRT outweigh the risks.
In addition, the general advice in the UK is that women with a history of breast cancer should avoid taking HRT.