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BACKGROUND Fibroepithelial lesions of the breast (FEL) are atypical lesions diagnosed on core-needle biopsy. The purpose of this study was to determine the rate at which FELs are upstaged to phyllodes tumor on excision, and to examine the clinical and radiological factors that may be predictive of upstaging. METHODS A retrospective review from the medical records of patients diagnosed with FEL on CNB at a single institution between 2010 and 2015 was performed. Patients diagnosed with benign or borderline phyllodes tumors were compared to those diagnosed with fibroadenoma. RESULTS Of 74 patients diagnosed with FEL, 48 underwent excision (64.9%). Of the 48 lesions excised, pathology revealed 30 fibroadenomas (62.5%), 14 benign phyllodes tumors (29.2%), and 4 borderline phyllodes tumor (8.3%). No malignant phyllodes tumors were identified. On preoperative ultrasound, heterogeneous echotexture (p = 0.03) and lack of internal vascularity (p = 0.03) were significantly associated with upstaging to phyllodes tumor. CONCLUSIONS Surgical excision of FELs yield a pathological diagnosis of benign and borderline phyllodes tumor in 37.5% of cases. A high BIRADs score (≥4b), heterogeneous echotexture and lack of internal vascularity on ultrasound may help predict upstaging to phyllodes tumor.