(ChemotherapyAdvisor) – The aromatase inhibitor letrozole more effectively reduced disease-free survival events, overall deaths, breast cancer recurrences, and distant metastases across all categories of body mass index (BMI) in postmenopausal women with early-stage breast cancer, results from the Breast International Group (BIG) 1-98 trial published in the Journal of Clinical Oncology online October 8 have shown.
At a median follow-up of 8.7 years, the results are also “in broad agreement that obesity is an independent adverse prognostic factor for death after breast cancer,” reported lead author Marianne Ewertz, MD, of the University of Southern Denmark, Odense, Denmark.
Previously, results of the Anastrozole, Tamoxifen Alone or in Combination (ATAC) Trial found that although tamoxifen was equally effective across all BMI categories, anastrozole was significantly less effective in postmenopausal women with a BMI exceeding 30 kg/m2, which suggested estrogen suppression with anastrozole may not be complete in obese women.
This study compared letrozole, an aromatase inhibitor that suppresses estrogen more effectively than anastrozole, with tamoxifen to examine the association of baseline BMI with risk of recurrence or death in 4,760 patients with breast cancer randomly assigned to 5 years of monotherapy with letrozole or tamoxifen in the BIG 1-98 trial with available information on BMI at randomization.
A total of 17% of patients died. Those who were obese (≥30 kg/m2) had slightly poorer OS (HR 1.19; 95% CI, 0.99–1.44) than patients with normal BMI (< 25 kg/m2). No trend in OS was observed in overweight (BMI 25 to <30 kg/m2) vs normal-weight patients (HR 1.02; 95% CI, 0.86–1.20). Treatment-by-BMI interactions were not statistically significant.
For OS comparing obese vs normal BMI, the hazard ratio was 1.22 (95% CI, 0.93–1.60) in the letrozole group vs 1.18 (95% CI, 0.91–1.52) in the tamoxifen group.