175P Prognostic role of body mass index (BMI) in patients with Human Epidermal growth factor Receptor 2 (HER2)–positive early breast cancer treated with adjuvant trastuzumab-containing chemotherapy

Abstract

High Body Mass Index (BMI) is a known risk factor for many types of malignancies, including breast cancer (BC). In some studies, adiposity has also been associated with worse outcomes in BC patients. However, the impact of excess weight on the prognosis of patients with Human Epidermal growth factor Receptor 2-positive (HER2+) BC remains unclear. We conducted a retrospective analysis to study the impact of BMI on relapse-free survival (RFS) and overall survival (OS) in surgically-resected HER2+ BC patients who received adjuvant trastuzumab-containing chemotherapy in our Institution between January 2008 and September 2018. Maximally selected rank statistics was used to estimate the best BMI and glycemia cut-off points capable of dividing our population according to the risk of recurrence. Cox regression models were used to assess the impact of BMI and other relevant variables on patient outcomes. Among 505 patients included in the study, 390 (77.2%) patients had a low (<27.77 kg/m2) BMI, while 115 (22.7%) patients had a high (≥27.77 kg/m2) BMI. Higher BMI was associated with worse RFS and OS at both univariate (HR for RFS: 1.88; 95% CI: 1.08 - 3.27, p=0.027; HR for OS: 1.85; 95% CI: 0.92 - 3.71, p=0.085) and multivariable analysis (HR for RFS: 2.26; 95% CI: 1.08 - 4.74, p=0.031; HR for OS: 2.25; 95% CI: 1.03-4.94, p=0.043). Blood glucose levels did not modify the impact of the BMI on patients’ risk of recurrence. A subgroup analysis showed that BMI effect on prognosis was limited to patients with HER2+ hormone receptor (HR)-negative BC. In a validation cohort of 132 patients treated with neoadjuvant trastuzumab-based chemotherapy we observed a trend towards worse RFS in the BMI-high vs. BMI-low group (p =0.056, log rank test). This is the first study to demonstrate the negative impact of high BMI on both RFS and OS in early-stage HER2+ BC patients treated with adjuvant trastuzumab-containing chemotherapy in the real-life setting. Further studies are needed to investigate the biologic mechanisms underlying our findings.