94MO the Prognostic and Predictive Effect of BMI in Postmenopausal HR+ Breast Cancer Patients Receiving (extended) Endocrine Therapy: DATA Trial Analysis

This study determines the prognostic and predictive effect of body mass index (BMI) on the disease-free survival (DFS) of postmenopausal hormone receptor-positive (HR+) breast cancer patients who received (extended) endocrine therapy. Patients with a BMI of ≥18.5 kg/m2 were identified from the randomised, phase III DATA trial (NCT00301457), which evaluated the use of six versus three years of anastrozole in postmenopausal women with HR+ breast cancer who were disease-free after two to three years of adjuvant tamoxifen. Patients were categorised as normal weight (18.5-24.9 kg/m2), overweight (25-29.9 kg/m2), or obese (≥30 kg/m2). The primary endpoint was DFS. Multivariable Cox regression analyses were performed. The prognostic impact of BMI was evaluated from date of randomisation, whereas the predictive impact of BMI on the efficacy of extended anastrozole was evaluated from three years after randomisation, i.e. treatment divergence (adapted DFS). Overall, 1,781 patients were included: 678 (38%) normal weight, 712 (40%) overweight, and 391 (22%) obese patients. After a median follow-up of 13.1 years, overweight and obese patients had a worse DFS when compared with normal weight patients (hazard ratio (HR)=1.16; 95% confidence interval (CI) 0.97-1.38, p=0.10; and HR=1.26; 95% CI 1.03-1.54, p=0.03, respectively). In women aged <60 years, overweight was associated with a worse DFS (HR=1.29; 95% CI 1.00-1.67, p=0.05) as was obesity (HR=1.83; 95% CI 1.36-2.46, p<0.001), but this was not observed in women aged ≥60 years (HR=1.04; 95% CI 0.82-1.33, p=0.72; and HR=0.94; 95% CI 0.72-1.23, p=0.63, respectively) (p-interaction = 0.009). The effect of extended anastrozole on adapted DFS did not differ between normal weight (HR=1.00; 95% CI 0.74-1.35, p=1.00), overweight (HR=0.74; 95% CI 0.56-0.98, p=0.04), and obese patients (HR=0.97; 95% CI 0.69-1.36, p=0.85) (p-interaction=0.24). In HR+ breast cancer patients aged <60 years at randomisation, overweight and obesity were adverse prognostic factors for DFS. In patients aged ≥60 years, this adverse prognostic effect was not observed. The effect of extended anastrozole on adapted DFS did not differ between BMI classes.