Important to know here is location. Apart from learning the histologic descriptions (which are boring as shit), neoplasia in the diaphysis is consistent with Ewing sarcoma. Osteosarcoma location is at the Metaphysis.

Ewing sarcoma cells look like small blue hypercromatic cells because they are neuroectodermal origin (PNET) and are therefore undifferentiated with high N:C ratio.

Also remember 22+11 translocation (EWS gene on chromosome 22 and the FLI-1 gene on chromosome 11)

Yeah, I thought the same @praderwilli (about the concentric layers)

Ewing sarcoma is the second most common bone malignancy in children. Histology is usually described as a small cell tumor with high N:C ratio.