Granular cell tumour of non-neural origin, ALK positive: Case report and literature review.

Non-neural granular cell tumour (NNGCT) is a rare cutaneous neoplasm characterised by the absence of S100 expression and a differentiation of uncertain lineage. We present the case of a 13-year-old male patient with a cutaneous lesion on the left wrist, initially diagnosed as pilomatrixoma. Histological analysis revealed a proliferation of spindle-shaped cells with eosinophilic granular cytoplasm and immunohistochemical positivity for ALK, NKI/C3, CD10, and CD68, with negativity for S100. ALK positivity in this case supports the hypothesis of a potential genetic alteration shared with other ALK-positive tumours. The patient had a favourable outcome following tumour excision, with no evidence of recurrence or metastasis. This case contributes to the characterisation of ALK-positive NNGCT and highlights its relevance in the differential diagnosis of cutaneous granular cell tumours.