 Flexner–Wintersteiner rosettes were first described by Simon Flexner (1863–1946), a physician, scientist, administrator, and professor of experimental pathology at the University of Pennsylvania (1899–1903).Flexner noted characteristic clusters of cells in an infantile eye tumor which he called retinoepithelioma.A few years later, in 1897, Austrian ophthalmologist Hugo Wintersteiner (1865–1946) confirmed Flexner’s observations and noted that the cell clusters resembled rods and cones.