HealthDay News — For postmenopausal women with breast cancer, extension of treatment with an aromatase inhibitor to 10 years is associated with improved outcomes, according to a study published online June 5 in the New England Journal of Medicine. The research was published to coincide with the annual meeting of the American Society of Clinical Oncology, held from June 3 to 7 in Chicago.

Paul E. Goss, MD, PhD, from Massachusetts General Hospital Cancer Center in Boston, and colleagues conducted a double-blind placebo-controlled trial to examine the effect of extended letrozole for an additional five years in a cohort of 1,918 postmenopausal women.

The researchers found that the 5-year disease-free survival rate was 95 and 91% in the letrozole and placebo groups, respectively (hazard ratio for recurrence or occurrence of contralateral breast cancer, 0.66; P=0.01). Five-year overall survival was 93 and 94%, respectively (hazard ratio, 0.97; P=0.83). The annual incidence rate of contralateral breast cancer was 0.21 and 0.49% in the letrozole and placebo groups (hazard ratio, 0.42; P=0.007). Patients receiving letrozole more often had bone-related toxic effects.

“The risk of disease recurrence and contralateral breast cancer was significantly lower among women who continued aromatase inhibitor for 10 years than among women who received placebo after the initial 5 years of aromatase-inhibitor therapy,” the authors write. However, “the rate of overall survival was not higher with the aromatase inhibitor than with placebo.”

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Several authors disclosed financial ties to pharmaceutical companies, including Novartis, which manufactures letrozole and contributed funding to the study.

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