Taking tamoxifen for longer reduces the risk of breast cancer

New research results show that women with oestrogen receptor positive breast cancer who take the drug tamoxifen for ten years rather than five, have a reduced risk of breast cancer recurring and better overall survival rates.

The findings of the ATLAS (Adjuvant Tamoxifen – Longer Against Shorter) study were presented this week at the renowned San Antonio Breast Cancer Symposium.

Tamoxifen is currently given to both pre and post-menopausal women and helps to prevent oestrogen receptor breast cancers from growing. It is usually given to women for at least five years.

However, the latest results from the ATLAS study show that while taking tamoxifen for five years reduces breast cancer mortality by almost a third, taking the drug for ten years halves breast cancer mortality in the second decade after diagnosis.

Christina Davies, M.D., a co-ordinator in the Clinical Trial Service Unit at the University of Oxford says, “Five years of adjuvant tamoxifen is already an excellent treatment that substantially reduces the 15-year risk for recurrence and death from estrogen receptor (ER)-positive breast cancer, but ATLAS now shows that 10 years of tamoxifen is even more effective.”

“The main additional benefit from continuing tamoxifen treatment is to reduce breast cancer mortality during the second decade after diagnosis,” she says.

The ATLAS study looked at 6,846 women with ER-positive breast cancer between 1996 and 2005. All the women had been using tamoxifen for five years, and the researchers randomly assigned them to continue treatment for another five years or to stop immediately.

After about eight years of follow-up, the researchers observed 1,328 breast cancer recurrences and 728 deaths after recurrence. The treatment allocation had little effect on either recurrence rates or death rates during the period five to nine years after diagnosis.

However, during the second decade following diagnosis, the women who continued tamoxifen treatment had a 25 percent lower recurrence rate and a 29 percent lower breast cancer mortality rate compared with women who stopped after five years.

Risk for death from breast cancer five to 14 years after diagnosis was 12.2 percent among those who continued use versus 15 percent among those who stopped — an absolute gain of 2.8 percent. The researchers observed the greatest benefit during 10 to 14 years after diagnosis.

Dr Davies noted that continuing tamoxifen use can increase side effects, with endometrial cancer being the most life-threatening.

“Many women with ER-positive breast cancer take tamoxifen, or some other adjuvant endocrine treatment, but the current recommendation is to stop after five years. The ATLAS study shows that protection against breast cancer recurrence and death is greater with 10 years than with five years of tamoxifen use. Women and their doctors should be aware of this evidence when deciding how long to continue tamoxifen, or any other endocrine treatment,” Dr Davies says.

The study was funded by Cancer Research U.K., the U.K. Medical Research Council, AstraZeneca, the United States Army and the European Union.

January 2013

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