Melanotic neuroectodermal tumor of infancy. A reexamination of a histogenetic problem based on immunohistochemical, flow cytometric, and ultrastructural study of 10 cases.

Ten cases of melanotic neuroectodermal tumor of infancy (MNTI) were studied. There were nine males and one female ranging in age from 2 weeks to 10 months; one patient was 8 years old. Sites of origin were the maxilla (five), epididymis (two), mandible (one), skull (one), and soft tissues of the cheek (one). Six tumors recurred from 1 to 18 months after diagnosis. One patient had widespread dissemination. Electron microscopic study of four cases showed cells with melanosomes at various stages of maturation, and cells with neuroblastic features, including neurosecretory granules and cytoplasmic processes. Nine cases of MNTI were studied immunohistochemically. Small neuroblastic cells and large cells in all cases were reactive for neuron-specific enolase (NSE), synaptophysin, HMB45, and dopamine-beta-hydroxylase, large cells in all cases and few small cells were reactive for cytokeratin (CK) and vimentin (VIM). Epithelial membrane antigen was observed in large cells in three cases, four cases expressed Leu 7 antigen, three were focally positive for glial fibrillary acidic protein, one for desmin, and one for chromogranin. All cases were nonreactive for retinol-binding protein, neurofilaments, alpha-fetoprotein, S-100 protein, and carcinoembryonic antigen. Five normal adult retinas were studied similarly; the pigmented epithelium of the retina was reactive for CK, VIM, HMB45, NSE, and S-100. DNA study, performed in eight tumors, revealed aneuploidy in two (DNA index = 1.7 and 1.8); these cases recurred within 1 month. No differences were observed according to site or behavior. MNTI is a primitive neuroectodermal tumor with polyphenotypic expression of neural and epithelial markers, melanin production, occasional glial, and rhabdomyoblastic differentiation, and no photoreceptor differentiation. It probably represents a dysembryogenetic neoplasm that recapitulates the retina at 5 weeks of gestation.