Sensitivity of BMI for the Screening of Obesity in Postmenopausal Breast Cancer Survivors

Objectives: Assess the accuracy of a BMI cutoff point >30 kg/m2 to identify obesity among postmenopausal breast cancer survivors and compare it with Percentage of Body Fat (PBF) and Fat Mass Index (FMI) using Dual-Energy X-ray Absorptiometry. Methods: Participants were recruited from the State Oncology Centre (CEO) in Hermosillo, México. Women were excluded if they had breast cancer surgery on both sides, had distant metastasis at the time of the interview and/or cosmetic surgical implants. Body weight and height were measured using a calibrated scale and stadiometer. BMI was calculated as weight in kilograms divided by height in squared meters. Body composition was determined by Dual energy x-ray absorptiometry (DEXA-Hologic QDR) to estimate percentage of body fat (PBF) and fat mass index (FMI). Youden index (YI), Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated. For the calculation of sensitivity, a 2x2 contingency table was used, taking the most direct markers of adiposity (FMI and PBF) as reference, to determine the ability of BMI to identify the presence of obesity in breast cancer survivors. Results: The sensitivity obtained is low, 53.49% according to PBF and 76.67% according to FMI. In comparison to both markers, BMI showed high specificity (100%) and high PPV (100%). However, it is important to note that the NPV of BMI was considerably lower when compared to PBF (16.67%) instead of FMI (70.83%). Moreover, the YI revealed that the BMI cut-off point yielding the highest sensitivity (97.67%) and specificity (100%) was >25.4 kg/m2 based on PBF. Conversely, a BMI cut-off point of >29.4 kg/m2 demonstrated a sensitivity and specificity of 86.6% and 100%, respectively. Conclusions: The BMI cutoff point of >30 kg/m2 shows insufficient sensitivity, making it less suitable for identifying obesity in postmenopausal breast cancer survivors.