Pediatric Brain Tumors: An Overview

Abstract

Although brain tumors are the second most common cancer in children, advances in treatment have lagged behind those of other forms of childhood cancer. Several factors unique to brain tumors account for the poor results: •¿ The inability to safely debulk many cen tral nervous system (CNS) tumors. •¿ The presence of the blood-brain barrier, which restricts access to the CNS of par enterally administered chemotherapeutic agents. •¿ The low mitotic rate of many CNS tu mors. •¿ The toxicity associated with high doses of CNS radiation therapy. These problems are compounded by limited experience with brain tumors in children.The annualincidenceinchildren younger than 15 years of age in the United States is 2.4 per 100,000, which means that brain tumors are diagnosed in approx imately 1,200 to 1,500 children each year.' The yearly accrual of the various histologic subtypes of brain tumors is, therefore, cor respondingly small. In addition, because only about 50 percent of children with brain tumors are referred to university or cancer treatment centers,2 therapeutic trials, by default rather than design, have been re stricted to small numbers of patients. Another complication is the lack of a universally accepted histologic classifica tion or grading system for brain tumors. The World Health Organization (WHO) classification has been inadequate for a substantial proportion of brain tumors in children. The lack of uniformity in clas sification results in the inability to accu rately evaluate prognosis based on histology from one center to another. Similarly, re ported responses to treatment are often dif ficult to assess. In addition, there are neither well established clinical and surgical staging criteria, nor universally accepted defini tions of response and relapse. As with other tumorsof childhood,stagingsystemsfor braintumorsmay establishguidelinesthat permit prognosis based on extent of disease at diagnosis and postoperatively. Medul loblastoma has been the only CNS tumor for which an effort has been made to cor relate surgical staging with prognosis. Subsequent evaluations have indicated that staging in this tumor may have prognostic significance.