AN UNUSUAL CEREBELLAR PRIMITIVE NEUROECTODERMAL TUMOR WITH T(11-22) TRANSLOCATION - PATHOLOGICAL AND MOLECULAR ANALYSIS

Peripheral primitive neuroectodermal tumors (PNETs) consistently demon strate a reciprocal translocation, t(11;22)(g24;q12). This translocati on 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 A lcian blue-positive material. Tumor cells were immunoreactive for neur on-specific enolase and synaptophysin. Electron microscopy revealed we ll-developed rough endoplasmic reticulum, cell processes with intermed iate filaments, microtubules, and dense core granules, and extracellul ar material reminiscent of mucopolysaccharide. Reverse transcriptase p olymerase chain reaction (PCR) revealed an 11;22 translocation-specifi c PCR product. Clinically the tumor was a cerebellar PNET with leptome ningeal dissemination and there was no evidence to suggest that it was metastatic. Histopathology, however, was indicative of an unusual PNE T that also manifested t(11;22) and was associated with an aggressive clinical course.