Granular cell tumor of the breast preoperatively diagnosed by fine-needle aspiration cytology: report of a case.

Granular cell tumors (GCTs) have a characteristic cytological appearance, and fine-needle aspiration cytology (FNAC) has been suggested to be the diagnostic modality of choice. However, the differential diagnosis has not yet been well described. We herein describe a rare case of GCT of the breast and discuss the differential diagnosis. A 53-year-old woman presented to our hospital with a left breast mass. In clinical and radiological examinations, the mass was suspected to be malignant. Cytologically, the tumor was composed of cohesive groups of cells with a syncytial appearance, and the cells contained abundant, finely eosinophilic cytoplasmic granules and small round-to-slightly-oval nuclei, thus suggesting the presence of benign GCT. The results of immunohistochemical staining supported the proposed deviation from Schwann cells. This case emphasizes the fact that GCTs are a rare but important possibility in the differential diagnosis of breast tumors, and that FNAC may provide clinically useful information on the management of such lesions.