Background: This study analyzes the association of body mass index (BMI) and prognostically relevant breast cancer (BC) characteristics in a country that has been rather spared of the global obesity epidemic. Patients and Methods: Based on 20-year data (1999-2009, n = 1,414) of the prospective relational BC database of the University Hospital Basel, Switzerland, the associations between BMI, tumor size and stage, histological subtype, grading, hormonal receptor status, HER2 status and ‘triple-negative' status were evaluated. Multivariate analysis considered BMI and patient's age. Results: The association between increasing BMI and the above-mentioned variables were as follows (results described in each case: Beta-coefficient or odds ratio, 95% confidence interval, p value): tumor size, (1) entire cohort: 0.03 (0.01-0.05), p < 0.001, (2) tumor found by self-palpation: 0.05 (0.03-0.07), p < 0.001, (3) tumor found by radiological examination: 0.03 (0-0.07), p = 0.044; advanced TNM stage: 1.16 (1.02-1.31), p = 0.022; histological subtype: 1.04 (0.89-1.22), p = 0.602; unfavorable grading: 1.11 (1.00-1.25), p = 0.057; positive estrogen receptor status: 0.95 (0.83-1.09), p = 0.459; positive HER2 status: 0.92 (0.74-1.15), p = 0.467; presence of a ‘triple-negative' carcinoma: 1.19 (0.93-1.52), p = 0.165. Consideration of only postmenopausal BC patients (n = 1,063) did attenuate the results, but did not change the direction of the associations with BMI. Conclusion: BMI was positively associated with TNM stage, grading and tumor size for tumors that were found by self-detection, as well as for those lesions detected by radiological breast examinations.
