neuroectodermal neoplasm neuroectodermal neoplasm a neuroectodermal neoplasm is a neoplasm or tumor of the neuroectoderm. they are most commonly tumors in the central or peripheral nervous system. neuroectodermal tumorspecialtyoncology tumors exhibiting neuroectodermal differentiation are classified into two main groups: group i tumors/neoplasms: neuroendocrine carcinomas. these show predominantly epithelial differentiation. they include pituitary adenoma and carcinoid tumor group ii tumors/neoplasms: nonepithelial neuroectodermal neoplasms. these are predominantly neural in origin. they include malignant melanoma, olfactory neuroblastoma and ewing's sarcoma.