round cell sarcoma

round cell sar·co·ma

obsolete term for an undifferentiated malignant neoplasm, believed to be of mesenchymal origin, composed chiefly of closely packed round cells.

round cell sarcoma

(1) A sarcoma (malignant tumour of mesenchymal origin) composed of round cells—e.g., epithelioid sarcoma, biphasic synovial sarcomas, some PEComas. The term is based on its histologic appearance and was used early in the diagnostic workup, before the results of immunohistochemical stains allow it to be slotted into a more specific category.
(2) An obsolete term for a lymphoma with round cells (lymphocytes) and a sarcomatoid stroma.
(3) Round cell tumour, see there. 
(4) Ewing sarcoma, see there.