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Ten years of tamoxifen almost halves deaths for common breast cancer

Risk of endometrial cancer 4 per 1000 and far outweighed by lives saved, say researchers

Caroline White

Wednesday, 05 December 2012

Treating one of the most common types of breast cancer with tamoxifen for 10 years rather than the usual five, curbs the likelihood of recurrence and almost halves the death rate, finds research published in The Lancet.

Tamoxifen taken daily for five years is the current standard treatment and is known to reduce death rates by around a third throughout the first 15 years after diagnosis, as the protective effects continue for at least a decade after the five years of treatment has ended.

In the Adjuvant Tamoxifen: Longer Against Shorter (ATLAS) trial, an international group of researchers, led by a team at the University of Oxford, investigated whether continuing to take tamoxifen for 10 years would reduce the breast cancer death rate still further.

They looked at the drug’s impact on recurrence and death in just under 7000 women with oestrogen positive disease. Of these, 3428 were randomly allocated to continue tamoxifen treatment for a further five years and 3418 were randomly assigned to five years of treatment.

The results showed that continuing tamoxifen for 10 years further reduced rates of recurrence and breast cancer death, but that the additional benefits took some years to emerge.

The risk of recurrence by year 15 was 21.4% in those allocated to continue tamoxifen, compared to 25.1% in the control group. Breast cancer mortality between 5 and 15 years was 12.2% in those allocated to continue tamoxifen and 15.0% in those who stopped after 5 years.

Tamoxifen has some side-effects, but the net effect on survival was relatively small, the findings showed.

The most significant side effect was an increased risk of endometrial cancer among women who had gone through the menopause, but the excess risk of dying of it by year 15 was only 0.4% in the 10 year treatment group compared with 0.2% in the 5 year treatment group.

There was no evidence of an increased risk of stroke during treatment with tamoxifen, despite the fact that the US Food and Drug Administration (FDA) lists this as a possible side-effect.

Lead author Dr Christina Davies of the University of Oxford, said: “Good evidence now exists that 10 years of tamoxifen in [oestrogen receptor] 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.”

She added: “While our results show a small increase in life-threatening side-effects for women who take tamoxifen for ten years rather than five, this increase is greatly outweighed by the reduction in breast cancer mortality.”

In a linked Comment, Professor Trevor Powles of the Cancer Centre London, said “If, as seems likely, the ATLAS findings will be reinforced next year, this should herald a change of practice, with the standard of care revised to 10 years rather than 5 years of treatment in patients for whom tamoxifen is indicated.”

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