Metastatic granular cell tumor to the breast diagnosed by fine needle aspiration cytology: A case report with review of the literature

Granular cell tumors (GCT) are mesenchymal neoplasms of Schwann cell/neural origin. Malignant granular cell tumors (MGCTs) represent <1‐2% of all GCT and defined as tumors demonstrating metastases or destructive local growth. Other clinical parameters suggestive of malignancy include rapid growth, size > 4 cm and necrosis. An apparently inconsistent set of histological features have been described in MGCT. Although the histologic parameters of a GCT are not always predictive of biologic behavior, the presence of atypical features may be indicative of an aggressive clinical behavior (recurrence and metastases). A preoperative estimate of features suggestive of malignancy is important for treatment and prognostication. Diagnosis and prognostication from preoperative fine needle aspiration (FNA) cytology is hampered by the fact that only a few case reports on cytologic features of malignant GCT have been published. We report a case of metastatic MGCT to breast and compare cytologic features to that of primary breast GCT and apocrine/histiocytoid variants of breast carcinoma.