Prognostic importance of cellular differentiation in medulloblastoma of childhood.

Medulloblastoma is the most common intracranial primitive neuroectodermal malignancy of childhood. Certain parameters are predictive of survival in children with medulloblastoma; however, tumor histology is of unclear prognostic value. A classification system, proposed by Rorke for all central nervous system (CNS) neoplasms composed of primitive neuroepithelial cells, was utilized in a review of 38 consecutive patients with newly diagnosed medulloblastoma. The classification is based on the concept that medulloblastoma is not unique to the cerebellum but is similar to tumors that may arise elsewhere in the CNS consequent to neoplastic transformation of primitive neuroepithelial cells. Cells forming the tumors may remain in the undifferentiated state or they may exhibit differentiation along glial, and/or ependymal, and/or neuronal lines. For purposes of simplification, the cases were divided into two major groups: those primitive neuroectodermal tumors (PNET's) which showed no evidence of cellular differentiation (PNET-U) and those that were differentiated (PNET-D). There were 20 cases in the PNET-U group and 18 in the PNET-D group. The 4-year survival rate was 70% for PNET-U, compared to 32% for PNET-D (p = 0.004). Only one of 10 children with PNET-D with differentiation along more than one cell line survived. Other factors, including age at diagnosis, tumor metastasis (TM) stage, and extent of surgical resection, were analyzed and were of prognostic importance; but histological features remained statistically significant within each subgroup.