Carboplatin in childhood brain tumors. A Children's Cancer Study Group Phase II trial. Between October 1985 and March 1988, Children's Cancer Study Group institutions entered 95 patients with recurrent brain tumors into a Phase II trial of carboplatin 560 mg/m2 every 4 weeks. Complete or partial responses were observed for one of 19 evaluable children with brainstem glioma, two of 14 with ependymoma, six of 19 with medulloblastoma or central nervous system primitive neuroectodermal tumor (PNET), and none of 15 with high-grade astrocytoma. Of 33 children with medulloblastoma, ependymoma, or central nervous system PNET, five of 12 with no prior cisplatin exposure had responses, and two of 21 with prior cisplatin exposure had responses (P = 0.03). Thirty-four percent of patients had absolute neutrophil count nadirs less than 500/microliters, and 37% had platelet count nadirs less than 25,000/microliters. Sixteen percent had moderate to severe otoxicity, 10% had nausea and vomiting, and none had nephrotoxicity. 