Giving breast cancer survivors hormone replacement therapy is safe, according to myth-debunking research.
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 dismissed the concerns, sparked by just two studies in the 1990s. They found there was no increased risk of recurrence for women on HRT.
The discovery gives hope to thousands who have survived breast cancer only to be plagued by hot flushes and reduced libido.
Many have been left to struggle through the menopause using natural remedies or nothing at all, campaigners say.
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 the patches, gels and implant.
Women 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.
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, she still advised caution when considering vaginal oestrogen for breast cancer survivors on aromatase inhibitors.
A Cancer Research UK spokesperson said further research was needed to confirm the Danish study’s findings.
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.