Although the tumor location is unusual (but head and neck seated), most of the other clinical, morphologic, immunophenotypic (focal combined expression of S100 protein, SMA, desmin, and myogenin) and oncogenic data suggest that this biphenotypic "oropharyngeal" sarcoma is closely related to the biphenotypic SNS spectrum.
On balance, if the following features are seen: (1) a small round blue cell tumor with histomorphology more atypical than that of Ewing sarcoma, (2) cytoplasmic CD99 staining, nuclear WT1 positivity, negative keratin, desmin and myogenin; and (3) EWSR1 rearrangement negative by FISH, then molecular testing for CIC-DUX4 sarcoma should be considered.
Furthermore, to identify the subtype of this sarcoma, the immunohistochemical staining of the tumor was performed with each of the various antibodies and the results are epithelial membrane antigen (-), H-caldesmon (-), desmin (+), smooth muscle actin (+), S-100 (-), myogenin (-), pan-keratin (-), and Ki-67 (positive rate: 20%).