Martin-Macintosh, Erica L.

86 Background: Phyllodes tumors (PT) are rare breast neoplasms confounding their systematic study and evidence-based management guidelines. There is little data on the sensitivity of preoperative core needle biopsy (CNB) and imaging findings in establishing a correct preoperative diagnosis. We undertook this study to evaluate the sensitivity of CNB histologic findings and imaging findings in preoperatively categorizing tumors as benign or borderline/malignant. Methods: We identified 47 patients who underwent surgical resection of a PT at our institution after a preoperative CNB between 6/2000-3/2012. Statistical analysis utilized Wilcoxon rank-sum, chi-square or Fisher’s exact tests, and 95% confidence intervals (CI) are reported. Results: 30 patients had a final diagnosis of benign and 17 of borderline/malignant PT. The latter were significantly more often palpable (76.5% vs 36.7%, p=0.01). No other clinical or radiologic feature predicted borderline/malignant subtype, although irregular shape on US was suggestive (70.6% vs 44.8%, p= 0.09). CNB diagnosis by tumor type is summarized in the table. No benign PT had ≥10 mitoses, necrosis or marked stromal atypia on CNB. No case with absent mitoses on preoperative CNB was a borderline/malignant PT; however 77% of benign PT did exhibit mitoses on CNB. Sensitivity of CNB for PT overall was 48.9% (95% CI: 35.3-62.8%) while it was 40% (24.6-57.7%) for benign PT and 17.6% (6.2-41.0%) for borderline/malignant PT. Conclusions: Marked stromal atypia, ≥10 mitoses and necrosis were rare on CNB, but suggestive of malignancy. No imaging or histology feature reliably distinguished between tumor types. Over one-third of borderline/malignant PT had a preoperative CNB diagnosis of fibroadenoma or cellular fibroepithelial lesion emphasizing the low sensitivity of CNB and the need for judicious consideration of definitive surgical excision. [Table: see text]