Granular cell tumor of the breast: Molecular pathology and clinical management.

Granular cell tumor is a rare condition that occasionally affects breast parenchyma: approximately, 5%-15% of all granular cell tumors represent 1:1000 of breast tumors. In this study, we reported a consecutive series of 12 patients with primary granular cell tumor of the breast observed at our institute, focusing attention on preoperative management, surgical approach, and long-term follow-up. Eight cases (8/12; 66.78%) presented with left-breast tumors; in the majority of patients (11/12; 91.7%), the lesion was identified in one of the upper quadrants. Specifically, upper intern quadrants (10 cases) were more affected. Surgical excision was performed in all patients. Mean diameter at pathologic section was 11.4 mm (range: 5-22). Tumor relapse was reported only in one case (8.3%). Mean follow-up was 98.1 months (range: 1-192). We proposed a model to explain the molecular mechanism of granular cell tumorigenesis associating to the high level of S100 protein. Management of primary granular cell tumor of the breast requires a correct initial diagnosis using breast imaging associated with core biopsy. Surgical procedure with wide resection or quadrantectomy requires a careful evaluation of breast margins.