Cores of tissues containing tumour.
Characterised by small round blue cells with a monomorphic appearance.
Prominent vascular pattern with some large vessels.
Fragment of necrotic tumour.
No differentiation.
In some fragments, tumour invades soft tissue.
No bone present. No osteoid formation.

CD99 - positive

Desmin - negative
myo-D1 - negative
myogen - negative
CD45, panCK, S100, PGP9.5, WT1 and ERG - all negative.

Overall appearances of a small round blue cell tumour without differentiation. Most in keeping with a Ewing sarcoma.