Peripheral and central primitive neuroectodermal tumors. A nosologic concept seeking a consensus

The term primitive neuroectodermal tumor is widely used in the literature for a group of small, round-cell tumors in the central and sympathetic nervous systems and soft tissues as well as a specific diagnostic term for individual neoplasms; however, the contention that these various clinicopathologic entities (neuroblastoma, medulloblastoma, and peripheral neuroepithelioma) are histogenetically related is an unproved hypothesis. Morphologic, cytogenetic, immunohistochemical, biochemical, and in vitro studies have established phenotypic similarities among these putatively related neoplasms whether they originate in the brain, adrenal gland, or soft tissues. Because one tumor resembles another in terms of its phenotypic expression, that does not necessarily imply a common histogenesis. This point has been made by previous investigators. The purpose of this review is to evaluate and discuss the present status of our understanding and some of the controversial aspects of this enigmatic category of neoplasms, mainly occurring in children, known as the primitive neuroectodermal tumors.