Is obesity an independent prognosis factor in woman breast cancer?

Background Breast cancer and obesity represent important public health issues in most western countries. A number of studies found a negative prognosis effect of obesity or excess of weight in woman breast cancer. However, to date, this issue remains controversial. The objectives of this study were to confirm the prognosis role of obesity on a large cohort of patients and to investigate a potential independent effect. Materials and methods We constituted a cohort of 14,709 patients who were recruited and treated at the Curie Institute (Paris) from 1981 to 1999. These patients were followed prospectively for a first unilateral invasive breast cancer without distant metastasis. Obesity was defined by a Body Mass Index (BMI) above 30 kg/m(2) according to the World Health Organization recommendations. Results Obese patients (8%) presented more extended tumors at diagnosis time suggesting a delayed breast cancer diagnosis. However, obesity appeared as a negative prognosis factor for several events in respectively univariate and multivariate survival analysis: metastasis recurrence (HR = 1.32[1.19-1.48]; HR = 1.12[1.00-1.26]), disease free interval (1.20[1.08-1.32]; 1.10[0.99-1.22]), overall survival (1.43[1.28-1.60]; 1.12[0.99-1.25]) and second primary cancer outcome (1.57[1.19-2.07]; 1.43[1.09-1.89]). Even if obese patients presented more advanced tumors at diagnosis time, multivariate analysis showed that there was a relevant independent effect. Other BMI codings, distinguishing overweight patients or using BMI as a continuous variable, showed a consistent correlation between BMI's value and prognosis effect. Interaction analysis revealed a more important obesity effect in the presence of tumor estrogen receptors and among limited extent tumors. Conclusions This survey confirms the prognosis role of obesity on one of the largest cohort by investigating several prognosis events. While independent obesity effect linked to hormonal disorders appeared consistent as obesity's mechanism, we stress that obesity prognosis effect was also related to breast cancer presentation at diagnosis time.