Overweight, obesity and breast cancer prognosis: optimal body size indicator cut-points

Background Evidence from the data provided in numerous published articles indicates that obesity and overweight can have a negative prognosis role in breast cancer. However, different Body Size Indicators (BSI) and cut-points have been employed and may partly explain discrepancies between the findings of various studies. Material and methods 14,709 women were recruited, treated and followed for a first unilateral breast cancer. After randomly splitting the patients' data into two groups, a maximum statistical outcome approach was used to select optimal BSI cut-points from a "training sample", when prognosis events were investigated. External validation was then carried out using a "validation sample", and agreement between the selected optimal BSI cut-points was assessed. Body Mass Index (BMI), weight (W), Ideal Weight Ratio (IWR) and Body Surface Area (BSA) were used, and were assessed at the time of diagnosis. Results The selected optimal BSI cut-points were reliable when overall survival, metastasis recurrence and disease free interval events were investigated. The chosen BMI cut-point values matched the overweight cut-point value given by the World Health Organization. Agreement between defined binary BSI was acceptable; however, it varied from "fair" to "very good". Analysis of second primary cancer occurrence and contralateral recurrence events was not conclusive. When local and node recurrence events were taken into account, the results were inconsistent and were linked to an unconfirmed relationship between stoutness and these prognosis events. Conclusions Efficient, optimal BSI cut-points indicate a poorer prognosis, illustrated by a shortened overall survival and an increase of metastasis recurrences, from a BMI value of 25 kg/mA(2), a W value of 60 kg, an IWR value of 20% and a BSA value of 1.7 mA(2). Further BSI cut-point investigations are needed, taking into account contralateral recurrence and second primary cancer events.