An unusual cerebellar primitive neuroectodermal tumor with t(11;22) translocation: pathological and molecular analysis.

Peripheral primitive neuroectodermal tumors (PNETs) consistently demonstrate a reciprocal translocation, t(11;22)(q24;q12). This translocation has not been found in PNETs of the central nervous system including the cerebellar medulloblastoma. We report an unusual cerebellar PNET in a 4-year-old boy in which tumor cells were surrounded by pools of Alcian blue-positive material. Tumor cells were immunoreactive for neuron-specific enolase and synaptophysin. Electron microscopy revealed well-developed rough endoplasmic reticulum, cell processes with intermediate filaments, microtubules, and dense core granules, and extracellular material reminiscent of mucopolysaccharide. Reverse transcriptase polymerase chain reaction (PCR) revealed an 11;22 translocation-specific PCR product. Clinically the tumor was a cerebellar PNET with leptomeningeal dissemination and there was no evidence to suggest that it was metastatic. Histopathology, however, was indicative of an unusual PNET that also manifested t(11;22) and was associated with an aggressive clinical course.