Primitive non-neural granular cell tumour of skin: report of a case

Abstract

<h3>Background</h3> Granular cell tumour of skin is an uncommon benign neoplasm of neural origin. However, a rare histologically similar but S100 protein negative tumour designated by Le Boit <i>et al</i>. in 1991 as ‘primitive non-neural polypoid granular cell tumour' has also been recognised and its cell lineage remains uncertain. <h3>Case report</h3> A 77-year-old male presented with a painless nodule on his right cheek. Histolopathology revealed an ulcerated dermal tumour with nodular architecture formed by plump spindle and epitheloid cells with prominent granular eosinophilic cytoplasm, vesicular nuclei and numerous mitoses. Immunohistochemical staining showed strong positivity for CD10 and NKI/C3, and focal positivity for HMB45 and MITF. Staining for S100, MelanA, tyrosinase, MNF116, p63, panCK, CK5/6, desmin, SMA, SOX10, CD31 and CD34 were negative. A diagnosis of primitive non-neural polypoid granular cell tumour was made. <h3>Discussion</h3> The limited published data suggest primitive non-neural polypoid granular cell tumours usually pursue an indolent course. They are negative for S100 (unlike conventional granular cell tumour and melanoma), cytokeratin, desmin and SMA, indicating no obvious line of differentiation. However, they are consistently positive for NK1/C3, a marker for lysosomes in granular cells. This case highlights the value of immunohistochemistry in distinguishing this tumour from malignant entities.