10-year results from clinical trial of extended letrozole therapy for women with HR+ breast cancer

In the updated results from NRG Oncology/NSABP B-42 trial through 10 years of observation, extending letrozole therapy for additional five years after five years of adjuvant endocrine therapy resulted in a statistically significant improvement in the 10-year disease-free survival (DFS) of postmenopausal women with hormone-receptor-positive breast cancer. The study continues to show no difference in overall survival with letrozole compared to placebo. The findings were presented at the 2019 San Antonio Breast Cancer Symposium, held December 10-14.

The NRG Oncology/NSABP B-42 trial enrolled 3,966 patients between September 2006 and January 2010. Patients were randomized to receive 2.5mg letrozole or placebo daily for 5 years after having undergone 5 previous years of hormonal therapy, (with either an aromatase inhibitor or tamoxifen followed by an aromatase inhibitor). In the original results of this phase III trial, presented at the San Antonio Breast Cancer Symposium in 2016, the beneficial effect of extended letrozole therapy on DFS did not reach statistical significance. The updated results, with median follow-up of 9.3 years, demonstrate a similar but statistically significant benefit for letrozole vs placebo (HR=0.84; 95% CI 0.74, 0.96; p=0.011). In addition, letrozole continues to provide a statistically significant improvement in breast-cancer-free interval (26% decrease in the risk of BCFI events) and distant recurrence (29% reduction in the risk of DR events). Overall survival rates, as in the earlier analysis, continued to show no significant improvement with letrozole. There were no significant differences in the risk of osteoporotic fractures and arterial thrombotic events between the letrozole and the placebo groups.

Our findings continue to suggest that careful assessment of potential risks and benefits is necessary for selecting appropriate candidates for extended letrozole therapy among patients with early-stage breast cancer."

Terry Mamounas, MD, of the Orlando Health UF Health Cancer Center, and lead investigator of the study

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