Recurrent Challenges in the Evaluation of Fibroepithelial Lesions

CONTEXT: The morphologic spectrum of mammary fibroepithelial lesions ranges from fibroadenoma, a common benign neoplasm, to phyllodes tumor, an uncommon lesion that can sometimes recur and metastasize. OBJECTIVE: To focus on problems encountered in the diagnostic evaluation of fibroepithelial tumors, highlighting the diagnostically relevant morphologic features and providing an update on the immunohistochemical profile and genetic alterations of these rare neoplasms. DATA SOURCES: A PubMed search of the English-language literature identified published reports on fibroepithelial lesions, with a special focus on phyllodes tumor. The results and conclusions of these studies form the basis of this review. CONCLUSIONS: The distinction between fibroadenoma and phyllodes tumor is usually not problematic, especially in excision specimens. In some cases, however, the diagnostic evaluation of fibroepithelial lesions can be challenging, especially if only limited material is available. Morphologic predictors of local recurrence of phyllodes tumor include cellularity and cytologic atypia, mitotic activity, positive margins, infiltrative borders, fibroproliferative satellite nodules, and past history of fibroadenoma. Predictors of distant metastasis include size, tumor necrosis, and stromal overgrowth. None of these parameters, however, constitutes a definite marker of malignancy. Presently, molecular and immunohistochemical techniques play a limited role in the diagnosis of fibroepithelial lesions.