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Case Reports

Abstract

INTRODUCTION

Melanoma with osteoclast-like giant cells (OGC) is an uncommon morphologic phenomenon. 2 undifferentiated melanoma with OGC which poses a diagnostic challenge have been reported in the literature. We report a further case of an undifferentiated melanoma with (OGC). In addition, there was focal cytokeratin expression suggestive of divergent differentiation. This was not previously described in the literature.

CASE DESCRIPTION

The case was a 95-year-old man who presented with an ulcerated 10mm nodule on the cheek. Histology showed severely sun damaged skin with an ulcerated tumour that invaded the deep dermis and associated with an epidermal collarette. There were sheets of pleomorphic epithelioid cells with irregular nuclear borders, vesicular chromatin, variable numbers of nucleoli, variably prominent nucleoli, and ample eosinophilic cytoplasm. There were also scattered osteoclast-like multinucleated cells, with similar nuclear cytomorphology. There was brisk mitotic activity. The immediate adjacent epidermis showed actinic keratosis.

The lesion was strongly and diffusely positive for PRAME. BRAF V600E was strongly positive in mononuclear cells but weak in giant cells. There was focal positivity for MNF116, Cam5.2, AE1/3 (weak to moderate) and CK5/6 (weak). S100 and CD163 stained giant cells and histiocytes only. The lesion was negative for SOX-10, MelanA, HMB45, MITF, CD63, CD10, SMA, desmin, CD34, ERG.

DISCUSSION AND CONCLUSION

Given the focal keratin positivity, a poorly differentiated squamous cell carcinoma with unusual BRAF V600E and PRAME positivity could be considered. However, given that the dysplastic squamous epithelium was negative for PRAME and BRAF V600E, on the balance a dedifferentiated melanoma with (OGC) is more likely.