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Medulloblastomas are classified by the WHO as embryonal tumors and comprise the most common of the malignant pediatric brain tumors while accounting for twenty percent of all pediatric brain tumors. The phenomenon of second malignancy is uncommonly seen in cases of uniform histology and are more rare when they are of a different histological type. The authors report two cases of infratentorial medulloblastomas that subsequently developed a grade IV glioma in one case, and a second medulloblastoma in the other. PRESENTATION: An eleven year-old female had been experiencing vision difficulty with right eye deviation and emesis. MRI showed a partially-enhancing posterior fossa mass lesion. Four years later, she was discovered to have a right parietal ring-enhancing lesion on routine surveillance. A four year-old female presented to our institution with a one-month history of headaches and emesis and a posterior fossa mass lesion. Three and a half years later, subsequent routine surveillance revealed a new enhancing lesion of the left temporal region with a higher Ki-67 labeling index. TREATMENT: Our first patient underwent sub-occipital craniotomy and gross-total resection for her medulloblatoma followed by chemoradiation under a COG protocol consisting of Vincristine, Cisplatin, and Cyclophosphamide and 23.4 Gy with a posterior fossa boost of 30.6 Gy. She underwent craniotomy for the GBM with GTR followed by maintenance chemotherapy. Our second patient underwent similar therapy with GTR for both lesions then was initiated after the second resection on a COG trial consisting of Bevacizumab, Temodar, and Irinotecan. Of note, both patients were on hormone therapy: GH and Lupron. CONCLUSIONS: We report two cases of infratentorial medulloblastoma with subsequent development of supratentorial lesions with discrepant histological profiles. A second malignancy of different cellular origin is rare, and molecular profiling of the two metachronous medulloblastomas will reveal whether they represent unique entities.

MB-37 * METACHRONOUS SUPRATENTORIAL INTRACRANIAL MALIGNANT TUMORS IN TWO PEDIATRIC PATIENTS WITH INFRATENTORIAL MEDULLOBLASTOMA ON HORMONE THERAPY