Histologic evaluation of neoadjuvant chemotherapy effect is a well-established prognostic indicator in
osteosarcoma and Ewing sarcoma arising in bone. Although tumor necrosis is a primary histologic response for the
treatment, secondary degenerative changes following necrosis are frequently shown in those tumors. We reviewed some
cases of Ewing sarcoma and osteosarcoma of bone with variable histologic alterations after chemotherapy. Secondary
degenerative changes seemed to be quite diverse; complete coagulative necrosis, fibrosis/hyalinization, vascular
enrichment, edematous stroma, variable shapes of bony trabeculae, and cystic/hemorrhagic changes replaced the tumors.
Morphologic changes of the primary tumor cells were not prominent. Such recognition of histologic patterns after
chemotherapy would be a great help for the evaluation of therapeutic effect.