Giving breast cancer survivors hormone replacement therapy is safe, research has suggested.
Doctors have for decades avoided recommending HRT to women who have beaten the disease over fears it would trigger a recurrence.
Danish scientists have now questioned the concerns, sparked by two studies in the 1990s.
They uncovered no increased risk of the disease returning in survivors taking HRT, specifically vaginal oestrogen.
The discovery gives hope to thousands who have survived breast cancer only to be plagued by crippling symptoms of the menopause. Many have been left to struggle through using natural remedies or nothing at all, campaigners say.
But the Danish study was small, and does not prove that all types of HRT are safe for breast cancer survivors.
A Danish study of 8,500 women with breast cancer has raised hopes more women can use HRT to treat symptoms of the menopause without increasing their risk of the disease returning (stock image of a breast cancer scan)
The new research, by Odense University Hospital, tracked 8,500 post-menopausal women.
All of the participants had been diagnosed with oestrogen receptor positive breast cancer, which thrive on the female sex hormone. About three quarters of all breast cancers in the UK are of this type.
HRT replenishes diminishing levels of oestrogen, hence why the cancer fears have left doctors afraid to dole out patches, gels and implants.
The drugs are currently available on prescription only.
Women in the study were given tamoxifen or aromatase inhibitors. Both drugs work by blocking oestrogen from working, helping slow breast cancer growth.
Slightly over 2,000 of the women took some form of HRT in the years following their cancer diagnosis.
WHAT IS THE MENOPAUSE?
Menopause is defined as the changes a woman goes through just before and after she stops her periods and is no longer able to get pregnant naturally.
Some women go through this time with few, if any, symptoms, around 60 percent experience symptoms resulting in behavioral changes and one in four will suffer severely.
Common symptoms include hot flushes, night sweats, vaginal dryness leading to discomfort during sex, disrupted sleep, decreased sex drive, problems with memory and concentration and mood swings.
Menopause happens when your ovaries stop producing as much of the hormone oestrogen and no longer release an egg each month.
In the UK, the average age for a woman to reach the menopause is 51, according to the NHS.
Participants were followed for up to a decade, or until a cancer recurrence or death occurred.
During the analysis, 1,333 (16 per cent) women had a breast cancer recurrence.
Of these 111 were taking vaginal oestrogen, 16 another form of HRT and 1,206 did not take any.
Calculations showed recurrence rates stood at 15.4 per cent in the vaginal oestrogen group and 17.1 per cent in the other HRT group.
This compared to a 19.2 per cent risk in the group not on HRT.
However, researchers did find a 39 per cent increased risk of cancer recurrence in a subset of women taking both vaginal oestrogen and aromatase inhibitors.
Dr Elizabeth Cathcart-Rake, a breast oncologist at the prestigious Mayo clinic in the US, said: ‘This large study helps to inform nuanced discussions between clinicians and breast cancer survivors about the safety of vaginal oestrogen therapy.
‘The results suggest breast cancer survivors on tamoxifen with severe genitourinary symptoms can take vaginal oestrogen therapy without experiencing an increase in their risk for breast cancer recurrence.
‘However, caution is still advised when considering vaginal estrogen for breast cancer survivors on aromatase inhibitors, or when considering menopausal hormonal therapy.’
A Cancer Research UK spokesperson said further research was needed to confirm the small Danish study’s findings.
Dr Channa Jayasena, consultant reproductive endocrinologist at Imperial College London, said the results look credible and suggest ‘future trials looking at the safety of HRT are warranted’.
However, he said: ‘It seems premature to recommend HRT to women after breast cancer based on just this study.’
Professor Debasish Tripathy, an oncologist at the University of Texas, told NewScientist: ‘I don’t think [these results are] conclusive enough to tell someone that they can safely use these oestrogen products.’
While the study raises hope that breast cancer survivors could use more forms of HRT, it comes as tens of thousands of women in the UK struggle to get hold of the menopause medication due to ongoing supply shortages.
There are about 56,000 breast cancer diagnoses in the UK each, the vast majority of which (99 per cent) are in women.
About 11,000 people die each year from breast cancer in Britain, with three quarters of people diagnosed with the disease surviving at least a decade.
Charity Breast Cancer Now estimates there are 600,000 breast cancer survivors in the UK.
In the US, 260,000 cases of breast cancer are diagnosed each year, with 42,000 deaths.
The most common sign of breast cancer is a new lump on breast. Women who notice a new lump in their breast or an area of thickened tissue should get it checked with their GP.