PNET: Primitive neuroectodermal tumor. One of a remarkable group of tumors that originate in cells from the primitive neural crest and share the same reciprocal translocation between chromosomes 11 and 22 and the same patterns of biochemical and oncogene expression. Some PNETs occur in the brain while others (the peripheral PNETs) occur in sites outside the brain such as in the extremities, pelvis, and the chest wall. PNETs in the brain can arise in the cerebral cortex or the pineal gland (pineoblastoma). The peripheral PNETs are part of the Ewing family of tumors which includes: Ewing tumor of bone; extraosseus Ewing tumor (tumor growing outside of the bone); primitive neuroectodermal tumor (PNET), also known as peripheral neuroepithelioma; and Askin tumor (PNET of the chest wall).