Undiff. Pleomorphic Sarcoma : Differential Diagnosis

Comments:
Differential Diagnosis of Undifferentiated Pleomorphic Sarcoma (UPS):

Pleomorphic Rhabdomyosarcoma: Microscopically, pleomorphic rhabdomyosarcoma (RMS) is characterized by haphazardly arranged large highly pleomorphic cells with one or more irregular hyperchromatic nuclei and abnormal mitoses. There may be areas with storiform or fascicular patterns. The cells have deeply eosinophilic cytoplasm and show some cell-to-cell molding.

There may be large irregular or tadpole-shaped rhabdomyoblasts which resemble the pleomorphic cells of UPS. Cells with cross-striations are less frequent than in embryonal RMS with pleomorphic or anaplastic features. Uncommon features include rhabdoid cells, phagocytosis by tumor cells, intracytoplasmic glycogen, and a lymphohistiocytic infiltrate. Myogenin and MyoD1 - which are nuclear regulatory proteins involved in skeletal muscle differentiation - are positive (nuclear staining).