Abstract P2-13-01: Impact of Body Mass Index (BMI) on the efficacy of aromatase inhibitors to suppress estradiol serum levels in postmenopausal patients with early breast cancer: a prospective proof of principle

Abstract

Abstract Background: BMI impacts on the efficacy of aromatase inhibitors (AIs) regarding disease outcome in patients with early breast cancer. We hypothesized that this clinical impact of BMI is driven by the inability of AIs to suppress estradiol (E2) serum levels to the same low level in obese compared to non-obese patients. Methods: 68 postmenopausal ER positive patients with breast cancer, scheduled to receive anastrozole or letrozole as adjuvant endocrine treatment were prospectively included in this study. Serum was taken before (T1) and 3 months after start with aromatase inhibitors (T2). Serum levels of FSH, LH, E2, glucose and insulin were analyzed immediately in the clinical routine lab and in a dedicated central lab able to measure E2 in serum at low concentrations with high sensitivity. Results: 40 patients were normal - or overweight (non-obese; BMI 18.5–29.9 kg/m2) and 28 patients were obese (BMI ≥ 30 kg/m2). A weak non-significant correlation between BMI and baseline E2 serum levels (r = 0.2, p = 0.2) translated into a strong negative, highly significant correlation between BMI and baseline FSH (r = −0.6, p < 0.01). After 3 months of AI treatment, a moderate correlation between BMI and E2 serum levels (r = 0.35, p = 0.05) and a moderate negative correlation between BMI and FSH (r = −0.34, p = 0.05) could be observed. Aromatase inhibitors significantly suppressed E2 serum levels in non-obese (T1: 18.9 pg/ml, T2: 9.0 pg/ml, p < 0.01) as well as in obese patients (T1: 20.2 pg/ml, T2: 12.5 pg/ml, p < 0.05). In addition an increase in FSH serum levels was observed in obese (T1: 50.0 mIU/ml, T2: 65.5 mIU/ml, p < 0.01) but not in non-obese (T1: 84.0 mIU/ml, T2: 84.6 mIU/ml) patients. However, after 3 months of AI treatment, E2 levels of obese patients were not at the same low level when compared to non-obese patients (E2 obese: 12.5 pg/ml vs. E2 non-obese: 9.0 pg/ml, p = 0.1). This difference translated into significantly lower FSH serum levels in obese compared to non-obese patients (FSH obese: 65.5 mIU/ml vs. FSH: 84.6 mIU/ml, p < 0.01). The significant effects of BMI on FSH serum levels could be detected both in the routine - as well as in the dedicated central lab. Conclusion: AIs are less efficient at suppressing E2 serum levels in obese when compared to non-obese women. The observed effect may contribute to the survival disadvantage of obese patients in adjuvant AI trials. FSH serum levels should be validated as high sensitive surrogate parameters for estradiol serum level suppression by aromatase inhibitors in postmenopausal patients with breast cancer. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-13-01.