Superficial small round-cell tumors with special reference to the Ewing's sarcoma family of tumors and the spectrum of differential diagnosis

Superficial/cutaneous small round-cell tumors comprise a heterogeneous group of neoplasms including sarcoma, carcinoma, melanoma, and lymphomas. Among superficial sarcomas, the Ewing's sarcoma family of tumors (ESFT) represents a poorly understood rare variant, having a behavioral difference characterized by a relative favorable prognosis. Several problems are still to be resolved in superficial ESFT, including the differential diagnosis between ESFT of bone (intraosseous or periosteal) with superficial infiltration and superficial ESFT with bone infiltration, especially in the fingers. Our aim is to review the most common types of small round-cell tumors included in the differential diagnosis of superficial ESFT, analyzing the histopathology, phenotype, and molecular alterations of each entity.