Biological factors of prognostic significance in primitive neuroectodermal tumors (PNETs) were evaluated in tumor specimens of 86 children examined at the Children’s Hospital of Philadelphia and University of Pennsylvania. Immunochemical evidence of glial differentiation (glial fibrillary acidic protein, GFAP) or neuronal differentiation (neurofilament proteins, NFPs) was associated with a 6.7-fold greater risk of relapse than tumors that did not express GFAP or NFPs. These biological characteristics of PNETs were as significant as tumor location and metastatic stage in predicting rate of relapse. 
COMMENT. The authors suggest that children with PNETs, especially cerebellar medulloblastoma, that express large amounts of glial fibrillary acidic protein (GFAP) are at increased risk for relapse and should be treated aggressively. Tumors should be classified as low or high risk based on both clinical factors, tumor location and metastatic stage, and biological factors, including GFAP expression.
The Mayo Clinical Update (12; 1:1996) notes that malignant brain tumors in children are increasing in incidence at a rate of 1.4% per year. For medulloblastoma, after radical resection followed by cisplatin and craniospinal irradiation, 5-year survival rate is 75%. A protocol involving gene therapy is about to be opened for the treatment of recurrences of some malignant tumors. The tumor is injected with cells that secrete a retroviral vector containing thymidine kinase gene isolated from herpes simplex virus. This therapy should result in killing of tumor cells with sparing of normal brain. New therapies are needed for PNETs since no effective treatment for children with recurrent medulloblastoma has been identified. Intensive therapies presently employed result in complications, including second malignancies, endocrine and growth dysfunction, and cognitive impairments. Basal-cell carcinoma, discussed below, is an example of a secondary malignancy induced by spinal irradiation for medulloblastoma. Low risk tumors, identified by the biological method, may be spared unnecessary aggressive and disabling therapy.