Tamoxifen for 10 years, not just 5, after breast cancer? Perhaps

December 5, 2012 | by Roberta Nichols

Tamoxifen can significantly reduce some women’s likelihood of breast cancer recurrence, and many women who have had what’s known as estrogen-receptor positive breast cancer take the controversial drug for five years after their initial treatment. A new study suggests that a 10-year regimen might lower their risk of recurrence even further.

In the worldwide study Adjuvant Tamoxifen: Longer Against Shorter, or ATLAS trial, 12,894 women with estrogen-receptor positive early breast cancer who had completed five years of treatment with tamoxifen were randomly assigned to take the drug for  10 years or stop at five years. The difference in risk of recurrence was dramatic.

“These results, taken with results from previous trials of five years of tamoxifen treatment versus none, suggest that 10 years of tamoxifen treatment can approximately halve breast cancer mortality during the second decade after diagnosis,” according to an international group of researchers, led by Dr. Christina Davies of the Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU) at the University of Oxford, UK, writing in the journal The Lancet.

But tamoxifen is not without considerable risks of its own, potentially leading to blood clots and uterine cancer.

The results warrant a discussion with patients, says Joanne Mortimer, M.D., F.A.C.P., director of the Women's Cancers Program at City of Hope, who was not involved in this research. Joanne Mortimer, M.D.

“The fact that five more years of tamoxifen are beneficial supports the fact that hormone-receptor positive breast cancer is a chronic disease,” says Mortimer. “This probably will not mean a lifetime of tamoxifen until clinical studies support that.”

She added: “The risk for these problems continues are long as you are on the drug."

Other drugs, known as aromatase inhihibitors, are also used to reduce the recurrence of breast cancer and, when they were introduced, were thought to be less toxic than tamoxifen.

“Of course, both drugs have side effects, both short term and long term," Mortimer says, pointing out that aromatase inhibitors can cause bone loss, joint pain and possibly changes in cholesterol. "So patients will need to weigh the toxicity profiles of the drugs.”

She adds: “It is always difficult for patients to take drugs in general – and those with side effects even more. Both tamoxifen and the aromatase inhibitors have non-compliance rates of 40 % by four years. So it may not be realistic to expect women to stay on a drug for 10 years."

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