Primary cutaneous Ewing's family sarcoma. Report of a case with immunostaining for glycoprotein p30/32 mic2.

The differential diagnosis of cutaneous small round cell malignancies is a relatively uncommon but recurrent problem that usually requires adjuvant techniques including special histochemical stains, immunohistochemistry (IHC), electron microscopy (EM), and cytogenetics (CG) to arrive at a definite answer. This report describes a case of a primary cutaneous malignancy that, after workup, fulfilled the criteria of extraskeletal Ewing's family sarcoma, which was corroborated by IHC with an antibody to glycoprotein p30/32 mic2 that is highly expressed in these neoplasms. The lesions consisted of a large nodular proliferation of poorly differentiated monotonous small round cells confined to the dermis and subcutaneous tissue. The cells had high nuclear to cytoplasmic (N/C) ratios, scattered prominent nucleoli, and indistinct cytoplasm. A periodic acid-Schiff (PAS) stain with and without diastase demonstrated abundant cytoplasmic glycogen. The glycogen was confirmed with EM, which did not show neurosecretory granules, but extensive sectioning of the tissue blocks demonstrated with light microscopy a single focus with pseudorosette formation. IHC was positive for monoclonal antibody (MAb) O13 to glycoprotein p30/32 mic2 and negative for lymphoid (CD45), neural (S-100, NF, GFAP), neuroendocrine (NSE), and muscle (MSA, desmin) markers. To the best of our knowledge, this is one of few reported cases of primary cutaneous (extraskeletal/extraosseous) Ewing's sarcoma (EEWS) and the first to use IHC with MAb O13, which recognizes the cell surface glycoprotein p30/32 mic2. This case further illustrates the continuum between EEWS and primitive peripheral neuroepithelioma and supports the unifying concept that these two entities are merely subtle morphologic variants of the same malignant neoplasm, which is better designated a Ewing's family sarcoma.