Answer: Epithelioid sarcoma

Histology: The tumor lesion on low power has the morphology of a palisaded necrotizing granuloma. There appears to be central collagenous necrobiosis, and the lesional cells simulate histiocytes surrounding this necrobiosis. However, the surrounding cells demonstrate fairly prominent nucleoli, and mitotic figures are evident. These cells label for both cytokeratin (shown below) and CD34, establishing the diagnosis of epithelioid sarcoma.

Discussion: A squamous carcinoma of the skin would be a major diagnostic consideration. However, attention to the age of the patient and CD34 immunoreactivity, as well as the characteristic architecture of the lesion, support the diagnosis of epithelioid sarcoma. Granuloma annulare would have necrobiotic granulomas with central mucin, and may simulate epithelioid sarcoma. However, granuloma annulare would not label for cytokeratins, and the surrounding cells would be histocytes with delicate nuclei and minimal mitotic activity. A rheumatoid nodule also may simulate an epithelioid sarcoma. Rheumatoid nodules feature palisading granulomas surrounding areas of fibrin. Again, the surrounding cells are macrophages with delicate nuclei which would not express cytokeratin and should not show mitotic activity.

Epithelioid sarcomas have a variety of morphologic patterns, including a fibroma-like variant, an angiomatoid variant, and a proximal rhabdoid variant. This is one of the sarcomas that does metastasize to regional lymph nodes, along with rhabdomyosarcoma, synovial sarcoma and clear cell sarcoma. These tumors often spread proximally up an extremity when they recur, necessitating amputation in many cases.

Reference(s):
– Adv Anat Pathol 2006;13: 114-121.