Taking tamoxifen for 10 rather than five years halves the risk of women dying from the most common kind of breast cancer, according to new research.
The “aTTom” study looked at almost 7,000 women with oestrogen receptor-positive breast cancer who, after five years of taking tamoxifen, either continued taking the drug for another five years or stopped treatment.
Among women who took tamoxifen for 10 years, 25% fewer had recurrences of breast cancer and 23% fewer died, compared to women who took the drug for just five years.
Lead researcher Dr Daniel Rea, from the University of Birmingham, said: “These results are important as they establish that giving tamoxifen for longer than the current standard of five years significantly cuts the risk of breast cancer returning.
“Tamoxifen is cheap and widely available so this could have an immediate impact,” he said.
Rare but serious side effects of tamoxifen include increased risk of endometrial cancer, blood clots, and stroke.
No increase in the incidence of stroke was observed in the study with 10 years of tamoxifen therapy, but endometrial cancer risk was higher.
The researchers estimated that for every endometrial cancer death that occurred as a side effect of long-term tamoxifen, there would be 30 deaths from breast cancer prevented.
They said the results established that “the benefits of taking tamoxifen for longer greatly outweigh the risks”.
Findings from the study, which was funded by Cancer Research UK and the Medical Research Council, were presented this month at the American Society of Clinical Oncology annual conference in Chicago.
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