Interesting soft tissue case

Got an interesting case, wondering what everybody thinks.

core bxs of a large L medial thigh mass (with destructive involvement of left pubis ramus) in a guy in his late 20s. also has multiple bilateral pulmonary lesions. the small blue cells infiltrating skeletal muscle are lymphocytes and plasma cells.

shows vimentin and CD56 staining but negative for a whole host of markers:

CD99-, desmin-, pankeratin-, AE1/AE3-, EMA-, S100-, GFAP-, CD117-, PLAP-, inhibin-, CD31-, p63-, melanoma markers -, synapto and chromogranin-, MSA/HHF35-, OCT3/4-, SALL4-.

also was negative (in 100 cells) for EWS translocations based on breakapart FISH probes on paraffinized tissue.

Our expert consultation called it an undifferentiated round cell malignant neoplasm.

Any thoughts???
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Vimentin

SMA

CD56

CD99

CD45