[Where does Ewing sarcoma end and begin - two cases of unusual bone tumors with t(20;22)(EWSR1-NFATc2) alteration].

The authors present two cases of Ewing-like sarcoma of the humerus and femur of a 12-year-old boy and a 28-year-old male, respectively. Identical morphology in both tumors consisted of multiple solid nests with a mosaic collection of small, round, uniform cells with clear cytoplasm and no apparent nuclear atypia. A monotonous structural arrangement, including both rich vascularity of bordering septae and significant admixtures of eosinophil leucocytes, resulted in a final organoid "neuroendocrine-like" pattern. Immunohistochemistry revealed diffuse strong CD10, CD99 and CD138 positivity. Detailed molecular analysis in both tumors confirmed translocation t(20;22) resulting in an EWSR1-NFATc2 fusion gene. Additionally, this translocation was accompanied by amplification of the proximal part of the genes and surrounding areas. Clinically, both neoplasms behaved aggressively and they were primarily chemoresistant. Four years later, the patient with the lesion in the humerus developed a massive local recurrence with a disruption of osteosynthesis. The last follow-up disclosed suspicious metastatic deposits in the lung. The boy with the femoral tumor underwent a total femoral prosthesis and there are no signs of local or systemic recurrence after 11 months of follow-up. The authors discuss the taxonomic placement of these rare examples of Ewing-like sarcoma family in the light of new molecular discoveries.