CD99 and primitive neuroectodermal tumor: Despite all the above, preliminary studies have shown that neuroendocrine tumors display a CD45−/CD56+ phenotype [32]–[35]; in turn, tumor cells from neuroblastoma coexpress GD2 [35], whereas primitive neuroectodermal tumors (PNET) coexpress CD57 and CD99, as well as CD56 [31], [34], [36]–[38], and rhabdomyosarcoma tumor cells are myogenin+[31], [39]–[41].