Background: The effect of body mass index (BMI) on the prognosis of metastatic breast cancer (MBC) has not been explored so far. Methods: The relationship between BMI (kg/m2) and progression-free survival (PFS) or overall survival (OS) was assessed in 489 patients with MBC enrolled in three clinical trials of first-line chemotherapy. World Health Organization BMI categories were used: normal, 18.5-24.9 kg/m2; overweight, 25-29.9 kg/m2; and obese, 30- kg/m2. Univariate PFS and OS curves were estimated; multivariate Cox analysis was conducted adjusting for age, menopausal status, performance status (PS), hormonal status and site, and number of metastases. Results: Overall, 39.9% of the patients were normal or underweight, 37.8% were overweight, and 22.3% were obese. Median age was 57 years (range 25-73); median PS was 0. Median PFS was 10.9 months [interquartile range (IQR) 5.5 to 19.9] in normal weight women, 13.0 months (IQR 7.8 to 23.7) in overweight, and 12.2 (IQR 7.1 to 23.0) in obese women, P = 0.17. Median OS was 32.0 months [95% confidence interval (CI), 14.5-88.3] versus 33.2 months (95% CI, 19.4-81.1) and 30.7 (95% CI, 17.6-50.8), respectively. In multivariate analyses, no statistically significant association between BMI category and PFS or OS was observed. Conclusions: In this study, BMI was not associated with the outcome of patients withMBCtreated with firstline chemotherapy. Impact: In the absence of any evidence in support of a prognostic role of obesity in patients with MBC treated with chemotherapy, dietary restrictions, medical interventions aimed at reducing BMI/insulin resistance, or specific anticancer treatment strategies do not seem to be appropriate.
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