Microscopic description and IHC:
The fine needle aspiration specimen shows small, bare nuclei with a granular background and uniform appearance. The surgical specimen shows small dark nuclei with abundant eosinophilic granular cytoplasm, which is a key feature for diagnosis. Granular cell tumors (GCT) are positive for S100, CD68, and SOX10.
Malignant GCTs will have 3 or more of the following: >2 mitoses / 10 high powered fields, increased nuclear/cytoplasmic ratio, pleomorphism, prominent nucleoli, necrosis, or cells that are spindled.
Discussion:
Granular cell tumors are common, usually benign neoplasms, with neuroectodermal differentiation thought to arise from Schwann cells. They can be found in all ages and many locations, but approximately 50% occur in the head and neck region; the tongue is the most encountered site.
Patients present with a painless mass, usually for less than a year in duration. They are treated by surgical resection and have a very favorable prognosis; approximately 10% have a recurrence. Malignant GCTs can occur but are rare.
References:
Cibas, E. & Ducatman, B. (2014). Cytology : Diagnostic Principles and Clinical Correlates. Philadelphia, PA: Elsevier/Saunders.
Fisher, C. (2011). Diagnostic Pathology: Soft Tissue Tumors. Salt Lake City: Amirsys.