Poorly differentiated squamous cell carcinoma with osteoclastic giant-cell-like proliferation

Although osteoclast giant-cell-like proliferations have been reported in a diverse range of human malignancies, to the best of our knowledge, they have never been described in cutaneous squamous cell carcinoma (SCC). Histologically, osteoclastic giant cell tumors within extraosseous malignancy resemble their bony and soft tissue counterparts, with round to spindle-shaped cells admixed with osteoclast-like multinucleate cells. These cells should be distinguished from sarcomatoid differentiation within a carcinoma; they have a benign morphology with a low nuclear to cytoplasmic ratio, minimal pleomorphism/mitoses and negative immunohistochemistry for cytokeratin. The authors report the rare occurrence of osteoclast-like giant cells (OGCs) and accompanying epithelioid histiocytes lacking overtly malignant features in association with a poorly differentiated SCC occurring on sun-damaged skin. Immunohistochemically, the area rich in OGCs was strongly positive for CD68 and completely negative for cytokeratin, whereas the poorly differentiated infiltrative area had the reverse immunophenotype and nuclear positivity for p63. The histological differential diagnosis and the origin of the proliferation are discussed in this article.