Introduction: Obesity affects 36 % of American women and is a well-documented breast cancer risk factor. Preoperative axillary ultrasound (AUS) is used routinely for axillary staging in newly diagnosed breast cancer patients; However, the impact of obesity on the usefulness of AUS is unknown. Our aim was to evaluate the effect of body mass index (BMI) on the performance of AUS. Methods: From our prospective breast surgery database, we identified 1,510 consecutive invasive breast cancers in patients undergoing primary surgery, including axillary operation, from January 2010 to July 2013. Preoperative AUS was performed in 1,375 cases (91 %). We analyzed patient, pathology and imaging data. Results: Median BMI was 27.4 and 479 patients (36 %) were classified as obese (BMI ≥ 30). Most tumors were T1 (71 %) and estrogen receptor-positive (87 %). AUS was suspicious in 401 (29 %) patients, of whom 374 had ultrasound-guided lymph node fine-needle aspiration (FNA). Overall, 124 patients (33.2 %) were FNA positive. FNA identified disease preoperatively in 35.8 % of node-positive obese patients. For all BMI categories (normal, overweight, obese), AUS was predictive of pathologic nodal status (p < 0.0001). AUS sensitivity did not differ across BMI categories, while specificity and accuracy were better for overweight (p = 0.001 and 0.008, respectively) and obese (p = 0.007 and 0.02, respectively) patients, than for normal-BMI patients. Conclusions: Despite theoretical concern regarding both potential technical challenges and obesity-related lymph node alterations, the sensitivity of preoperative AUS for detecting nodal metastasis was similar in obese and non-obese patients, while specificity was better in obese patients. Preoperative AUS is valuable for preoperative nodal staging of obese breast cancer patients.
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