A randomized phase III clinical trial, MA.17R found that postmenopausal women with early breast cancer benefit from extending aromatase inhibitor (AI) therapy with letrozole (Femara) from 5 to 10 years. Following five years of an AI and any duration of prior tamoxifen, women who received letrozole for five additional years had a 34% lower risk of recurrence than those who received placebo. The trial was led by the Canadian Cancer Trials Group, with participation from the National Clinical Trials Network. These results were discussed in ASCO’s Sunday, June 5, 2016 Plenary Session, which featured four abstracts deemed to have the greatest potential to impact patient care, out of the more than 5,000 abstracts featured at the 2016 American Society of Clinical Oncology (ASCO) Annual Meeting (June 3-7) in Chicago, Illinois. “Women with early-stage hormone-receptor-positive breast cancer face an indefinite risk of relapse,” said lead study author Paul Goss, M.D., F.R.C.P., Ph.D., director of Breast Cancer Research at Massachusetts General Hospital in Boston, Massachusetts and Professor of Medicine at Harvard Medical School. “The study provides direction for many patients and their doctors, confirming that prolonging aromatase inhibitor therapy can further reduce the risk of breast cancer recurrences. Longer AI therapy also showed a substantial breast cancer preventative effect in the opposite, healthy breast.” Overall survival was not significantly different in MA.17R between the two groups, but Dr. Goss notes that because of the slow chronic relapsing nature of hormone-receptor positive breast cancer, overall survival has proved difficult to demonstrate in clinical trials. Because of this, most endocrine therapies for breast cancer have gained regulatory approval based solely on improvement of disease-free survival.
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