Dermal non-neural granular cell tumour (so-called primitive polypoid granular cell tumour): a distinctive entity further delineated in a clinicopathological study of 11 cases.

AIMS

Cutaneous and soft tissue granular cell tumour is a well-characterized benign neoplasm of neural origin. However, there remains a subcategory of granular cell tumour, first described by Le Boit as 'primitive polypoid granular cell tumour', that shows no obvious line of differentiation. The aim of this study is to further the characterization of this lesion by undertaking a clinicopathological review.

METHODS AND RESULTS

Eleven cases of dermal non-neural granular cell tumour were retrieved from one of the authors referral archives (E.C.) and both the histology and immunohistochemistry reviewed. Clinical data with follow-up were obtained from the referring pathologists. The lesions most commonly occurred in young to middle-aged adults (nine cases, median = 33 years, age range 6-56 years), with a slight female predominance. They presented as painless nodules, mainly on the extremities or face. Local excision was the treatment of choice and up to date follow-up reveals no sign of recurrence. Histologically, eight cases were polypoid, while three cases were endophytic. The tumours were composed of elongated spindle-shaped to polygonal or round cells with prominent granular cell change, and tumour nuclei showing mild focal atypia to rare moderate atypia. Mitotic activity ranged from one to nine mitoses per 10 high-power fields (median = 2, mean = 3.8). Immunohistochemical labelling of the tumour cells demonstrated expression for NKI-C3 (n = 11), focal, weak positivity for CD68 (n = 10) and FXIIIa (n = 2). There was negative staining for S100 protein, smooth muscle actin, Melan-A, CD34, desmin and cytokeratin.

CONCLUSIONS

This analysis of 11 cases contributes to the characterization of this recently described entity, which despite some atypical histological features and no obvious line of differentiation, behaves in a completely indolent fashion.