Body mass index (BMI) and prognosis in women with metastatic breast cancer (MBC)

Background: Obesity is an acknowledged risk factor for the development of breast cancer and an adverse prognostic factor in those women who have already been diagnosed with breast cancer. However, the effect of obesity on the prognosis of MBC women has not been explored so far. With these premises, the aim of this study was to evaluate the influence of BMI on the prognosis of MBC patients receiving first line chemotherapy. Methods: The relationship between BMI (kg/m2), progression free (PFS) and overall survival (OS) was assessed on 698 MBC patients enrolled into 3 clinical trials (2 phase III and 1 phase II) of first-line chemotherapy. WHO BMI definitions were used: normal 18.5-24.9 kg/m2, overweight 25-30 kg/m2, obese >30 kg/m2. PFS and OS were calculated by Kaplan-Meier estimation; multivariate Cox analysis was performed adjusting for age, menopausal status, PS and study. Results: Information on BMI at the time of study entry, was available on 489 women. All patients received first line chemotherapy regimens including anthracyclines and taxanes, either in sequence or combination. Median follow up was 18 months (range 0.4 to 88.3). Overall, 40.3% of the patients were normal, 38.2% were overweight and 21.5% were obese. Median age was 57 years (range 25 to 73); PS was 0 in 93% of the patients. A non significant trend toward improved PFS was found in overweight women: median PFS was 13.1 months (95% CI 11.0-15.2) in BMI 25-30 versus 10.8 months (8.9-12.6) in BMI < 25 and 12.2 (95% CI 10.4-14.0) in BMI > 30, p=0.2. Median OS was 32.0 months (95% CI 24.9-39.1) in BMI < 25 versus 32.9 (95% CI 27.7-38.1) in BMI 25-30 and 30.7 (95% CI 24.3-37.0) in BMI >30, p=0.8. By multivariate analysis, none of the considered variables was significantly associated with differences in PFS and/or OS. Conclusions: In this study BMI at baseline was not significantly associated with the outcome of MBC patients treated with first line chemotherapy; however, a non significant trend for an improved PFS was observed in overweight women as compared to normal weight and obese patients. These data suggest that overweight should not be regarded as an adverse prognostic factor at least in MBC patients, already burdened by a diagnosis of advanced disease.