[Retinoblastoma: cell origin and differentiation]

50 retinoblastoma paraffin blocks were studied immunohistochemically (NSE, GFAP) and histochemically (colloidal-iron, RNA), and 13 cases by EM. The Rb cells demonstrated varying degrees of positive or negative reaction to NSE, most F-W and H-W rosettes being positive and the fleuretes weakly positive or negative. The GFAP positive cells were mainly found in the periphery of the tumor mass and around the blood vessels, and sparsely among the NSE positive cells. Fleuretes were clearly shown by RNA-Brachet staining. F-W rosettes and fleuretes showed similar ultrastructures as the photoreceptor of normal retina. The results confirmed that retinoblastoma originates from the retinoblast with potential of differentiation into photoreceptors and neurons. The glial components pertained to reactive gliosis, however, the rare possibility of forming a small portion of the tumor could not be ruled out.