Granular Cell Tumour

A granular cell tumour is an uncommon, usually benign soft-tissue tumour of Schwann-cell, that is neural, origin, which is why it stains positive for S100 and SOX10, and it is composed of cells with abundant granular eosinophilic, lysosome-rich, cytoplasm. It classically arises in the tongue, but also in the skin and soft tissue of the trunk and limbs and, uncommonly, in the viscera, typically as a small, firm dermal or subcutaneous nodule. Two things guide my management. First, the vast majority are benign and are cured by complete surgical excision with clear margins; very small lesions can be monitored in selected cases. Second, I would specifically assess for the rare malignant variant, which is the dangerous one: features that raise concern are a large size, often over about four to five centimetres, rapid growth, necrosis, increased mitoses and pleomorphism, and infiltrative margins, and a malignant granular cell tumour has a high risk of recurrence, metastasis and mortality. So a small, slow-growing, bland lesion is treated by complete local excision, whereas a large or rapidly growing or histologically worrying lesion warrants wide resection with clear margins and surveillance, managed at a specialist sarcoma centre. I would also be aware of a diagnostic pitfall: the epithelium overlying a cutaneous or mucosal granular cell tumour often shows pseudoepitheliomatous hyperplasia, which can be mistaken for squamous cell carcinoma on a superficial biopsy, so adequate sampling with S100 and SOX10 confirmation is important to avoid over-treatment.