Changes in Breast Cancer Treatment After ATLAS Trial Reveals Ten Years of Tamoxifen Better Than Five

According to the recently published results of the Adjuvant Tamoxifen: Longer Against Shorter (ATLAS) trial, 10 years of Tamoxifen treatment instead of the standard five years further reduces the long-term chances of recurrence and risk of dying from cancer. The study was published in The Lancet in December 2012, and simultaneously presented at the San Antonio Breast Cancer Symposium.

The study was conducted by an international group of researchers on 6,846 women with estrogen-receptor (ER) positive breast cancer. All women had been taking tamoxifen therapy for five years. For the study, half the women were assigned to a control group that discontinued the drug, while the other half continued taking tamoxifen for an additional five years. The researchers found a 10-year tamoxifen therapy reduced breast cancer recurrence and death than when taken for five years. These results, taken together 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.
The risk for breast cancer recurrence in the 10 years after the study began was 21.4% in women taking tamoxifen for 10 years and 25.1% in the control group.

Researcher, Richard Gray, Msc, noted, “For both recurrence and breast cancer mortality, there was little additional benefit during years 5 to 9, but after that there was a very definite effect. After year 10, we found very clear and significant benefit from having continued the treatment.” Researcher Christina Davies, MD, said, “Five years of adjuvant tamoxifen is already an excellent treatment that substantially reduces the 15-year risk for recurrence and death from ER positive breast cancer, but the ATLAS trial now shows that 10 years of tamoxifen is even more effective. The side effects of tamoxifen are well documented, which are an increased risk of uterine cancer and blood clots in the lungs. The most significant side effect was an increase in risk of endometrial cancer, although its effect on survival was relatively small. In the study, the increased risk of death from endometrial cancer was 0.4% compared to 0.2% in the control group.

The study is expected to change the practice of breast cancer treatment. In New York City, Dr. Maura Dickler in the Breast Cancer Medicine Service at the Memorial Sloan-Kettering Cancer Center said she would begin prescribing tamoxifen for 10 years, especially for high-risk, lymph node-positive, premenopausal women who typically discontinue endocrine therapy after five years.

Dr. Paromita Datta, medical director of the Breast Care Clinic at Aurora Breast Center in San Antonio, Texas, said, “Currently in my practice, postmenopausal patients with invasive cancer who completed 5 years of tamoxifen, will be switched to an aromatase inhibitor for 5 years. I would continue premenopausal patients on five more years (total of 10 years) of tamoxifen. The course of treatment will be dependent on the patient’s co-morbidities, tolerance for medications etc.”

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