Tamoxifen use 'should double' to stop breast cancer returning
A decade's treatment with tamoxifen could stop the return of breast cancer for many more women than the current recommendation for five years, say researchers.
University of Oxford scientists say the doubling cuts both the risk of the cancer returning and deaths from the disease.
Writing in The Lancet, they say this outweighs the risk of side effects.
Cancer Research UK said the study added important clarity.
Tamoxifen tablets have long been part of the daily routine for women in the years after remission from 'ER-positive' breast cancer.
ER-positive tumour growth is accelerated by the female sex hormone oestrogen, and tamoxifen blocks the hormone.
An international group of scientists, led by Dr Christina Davies from the University of Oxford, looked at the effect of sustained tamoxifen on the likelihood that cancer would return.
They looked at 6,847 women with the ER-positive version of the disease, half of whom were given tamoxifen for the standard five year period, and half who continued with the drug until the 10 year mark.
The results found that cancer returned in a quarter of the women given five years of tamoxifen. That fell to 21.4% in those given ten years of the drug.
Deaths from breast cancer was also significantly reduced, from 15% of those on the five-year programme, to just over 12% of those given 10 years.
While the changes are only a few percent, with more than 40,000 women diagnosed with breast cancer in the UK alone every year, a large proportion of whom have 'ER-positive' cancer, it could mean a significant decrease in the number whose cancer returns.
The report authors said: "Good evidence now exists that 10 years of tamoxifen in ER-positive breast cancer produces substantial reductions in rates of recurrence and in breast cancer mortality not only during the first decade, while treatment continues, but also during the second decade, long after it has ended."
The drug does cause side-effects in some patients, including, rarely, cancer of the lining of the womb, but the scientists said that the increased chance of preventing breast cancer returning far outweighed the risk.
Dr Caitlin Palframan, head of policy at Breakthrough Breast Cancer, said: "ER-positive breast cancer is the most common type of breast cancer and so improving treatment and getting the most out of the effective treatments we already have is key.
"This trial is great news for women with this type of breast cancer as it suggests that taking the commonly used drug, tamoxifen, for longer could save more lives with minimal additional side effects."
Other scientists say that 10 years could now become the standard for treatment.
Prof Trevor Powles, from Cancer Centre London, said that this, and other studies due to report next year, "should herald a change in practice".
The National Institute for Health and Clinical Excellence said: "We do not generally make recommendations relating to how long a patient should receive tamoxifen; that decision should be made by a doctor according to their professional judgement and in discussion with their patient, not least because there are continuing trials in this area.
"We review our guidance regularly to ensure it remains based on the best, most up-to-date evidence available and, when we come to update our guidelines on the diagnosis and management of breast cancer, we will take all new evidence into consideration."
Martin Ledwick, from Cancer Research UK which funded the study, said: "This important study adds further clarity to the question about the length of time women should take tamoxifen.
"Although treatment for hormone receptor positive breast cancer has become more complex in recent years with some women receiving aromatese inhibitors, these results will help in deciding the length of treatment for women who are prescribed tamoxifen alone."