Subtentorial tumors with rosettes are predominantly medulloblastomas (Figure 19), which are synaptophysin and NeuN positive, with a minority of such subtentorial tumors being the embryonal tumors with multilayered rosettes (ETMR), previously referred to as primitive neuroectodermal tumors (PNET) (Figure 19) which are synaptophysin negative and have a patchy vimentin expression. The gene discussed is SYP; the disease is primitive neuroectodermal tumor.