Ultrastructure of Ewing's tumour

Summary Tumour tissue surgically excised from 10 patients bearing Ewing's tumour of bones was examined electron microscopically and histoenzymologically. In all cases the tumour was composed of polygonal cells with cytoplasm poor in organelles but with conspicuous aggregates of glycogen particles. There were numerous intercellular connections of desmosomal type and a distinct cell membrane bound positivity for alkaline phosphatase activity. In two cases in which there was a negative reaction for alkaline phosphatase, the lack of enzyme activity might have been related to cytotoxic treatment carried out for several months immediately before excision of the tissue used for histoenzymological studies. The problem of histogenesis of Ewing's tumour remains unresolved although some of the present findings support a haemangiogenic origin of the tumour.