Cytologic "differentiation" in childhood rhabdomyosarcomas following polychemotherapy.

The effectiveness of polychemotherapy in young patients with rhabdomyosarcomas has been well established. The morphologic alterations in the tumor tissue, however, have not been widely reported. Therefore, in a group of 15 patients from 1 to 24 years of age, specimens of tumor tissue obtained before and after polychemotherapeutic treatment were compared. No morphologic changes, other than fibrosis and necrosis, occurred in patients who initially had virtually undifferentiated tumors. When moderately or well-differentiated areas were present in the initial specimens, these areas showed proportionate increases in the follow-up specimens. Moreover, the cellular characteristics of round rhabdomyoblasts and strap cells with or without cross-striations became more distinct after treatment. However, cell types that were not present in the initial specimens were never found in follow-up specimens. It was concluded that the major role of polychemotherapy is the selective destruction of undifferentiated tumor cells; further differentiated cells are stimulated either directly or indirectly to reach their maximal inherent differentiation levels, but it does not appear that transitions from one cell type to the other occur.