Impact of body mass index on the clinical outcomes of patients with HER2-positive metastatic breast cancer

Background Overweight and obesity are associated with an increased risk of developing many types of cancer, including breast cancer. Moreover, increased body mass index (BMI) seems to be associated with a worse prognosis in patients with HER2-positive early breast cancer. However, little is known about the impact of BMI on the clinical outcomes of HER2-positive metastatic breast cancer (MBC). Methods This was a multicenter retrospective cohort study including 329 consecutive patients with HER2-positive MBC treated with first-line trastuzumab-based regimens. BMI at the time of MBC diagnosis was collected. World Health Organization BMI categories were used: underweight <18.5, normal 18.5–24.9 Kg/m2, overweight 25–29.9 Kg/m2, and obese ≥30 Kg/m2. The analyses were conducted using two categories: BMI < 25.0 (normal/underweight) and BMI ≥ 25 (overweight/obese). Progression-free survival (PFS) and overall survival (OS) rates were estimated using Kaplan-Meier method. Univariate and multivariate survival analyses were performed using the Cox's proportional hazards model. Disease response to therapy was analyzed using univariate and multivariate logistic regression. Results Overall, 176 (53.5%) patients were normal/underweight and 153 (46.5%) overweight/obese. Median PFS was 14.8 months in BMI < 25 group and 15.7 months in BMI ≥ 25 group (adjusted-HR 0.88; 95% CI 0.66–1.17; p = 0.387). Median OS was 58.6 months in BMI < 25 group and 52.6 in BMI ≥ 25 group (adjusted-HR 0.88; 95% CI 0.59–1.31; p = 0.525). Overall response rate was 71.7% and 65.9% (p = 0.296) and clinical benefit rate was 82.1% and 83.3% (p = 0.781) in BMI < 25 and BMI ≥ 25 groups, respectively. Conclusions BMI does not seem to be associated with clinical outcomes in HER2-positive MBC patients.