This pathology commentary focuses on the diagnosis and key features of Granular Cell Tumor (GCT), particularly when occurring in the oral cavity (tongue). The speaker emphasizes the critical diagnostic pitfall: GCT often induces overlying reactive squamous hyperplasia that can closely mimic invasive squamous cell carcinoma (SCC), potentially leading to unnecessary surgical procedures. The video details the characteristic morphology of GCT cells (abundant granular cytoplasm, syncytial growth, and infiltration between collagen bundles). A crucial takeaway is that perineural involvement, present in approximately 90% of GCT cases, is a common and benign feature. The presentation concludes by identifying key immunohistochemical stains (S100, SOX10, and CD68, the lysosome marker responsible for the granular appearance) and markers that raise concern for rare malignant variants (mitotic activity, large nuclei).
Granular Cell Tumor (GCT): Pathology and Differential Diagnosis
0:03 The Diagnostic Trap: Lesions in the oral cavity (e.g., tongue) showing atypical squamous nests growing down (reactive change) can be mistaken for invasive squamous cell carcinoma (SCC).
0:20 Key Warning/Differential: If a lesion on the tongue appears to be SCC, always check the submucosa/dermis for nests of granular cells. Granular Cell Tumor (GCT) frequently induces a brisk, overlying pseudo-carcinomatous epidermal hyperplasia (suit-up reaction) that mimics SCC.
1:02 Cellular Morphology: GCT cells feature an abundant granular cytoplasm, round nuclei, and tend to merge together in a syncytial pattern (cell borders are difficult to distinguish).
1:13 Growth Pattern: GCTs grow by "oozing" into the spaces between dermal collagen bundles and can infiltrate deep tissues, including muscle. Although generally benign, local recurrence is possible, and very rare malignant examples exist.
1:37 Perineural Involvement (Crucial Takeaway): Perineural involvement (cells surrounding nerves) is seen in up to 90% of GCT cases. This is a benign finding and should not be misinterpreted as invasion or malignancy. GCTs are derived from nerve sheath cells, similar to schwannomas.
2:07 Malignant Features: Indicators that should prompt concern for rare malignant GCT include marked mitotic activity and large, atypical nuclei.
2:18 Immunohistochemistry (IHC): GCTs stain positive for S100 and SOX10 (neural markers).
2:23 Basis of Granularity: The abundant granularity of the cytoplasm is due to lysosomes.
2:35 IHC Stains (Lysosome Marker): GCTs are intensely positive for CD68, which is a lysosome marker (often taught incorrectly as solely a histiocyte marker).