Melanotic Neuroectodermal Tumor of Infancy (MNTI) shows dual epithelioid and neuroblastic differentiation. It has a biphasic appearance. 1) Epithelioid cells: It consists of a population of larger polygonal to cuboidal epithelioid cells (right half of image) forming nests, trabeculae, or pseudoglandular arrangements. They have varying amounts of melanin pigment and are positive for keratin, HMB-45, and tyrosinase. Ultrastructurally, they show features of epithelial and melanocytic cells containing both immature and mature melanosomes. 2) Neuroblastic cells: The second component consists of nests and sheets of small, round blue neuroblastic cells (left half of image) in a fibrillary background. These cells are positive for NSE, synaptophysin, and occasionally chromogranin. S-100 is negative in both cell populations. In some areas, one sees a single layer of epithelioid cells intimately associated with groups of neuroblastic cells.