Cynthia Y. Xu ^1,2* Craig A. Beers ^2,3 Crystal L. Hann ^2,3 Ronald C. Ramos ^1,2*

• ¹ Division of Neurology, Department of Medicine, Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada
• ² Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada
• ³ Department of Radiation Oncology, Juravinski Cancer Centre, Hamilton, Ontario, Canada

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a rare central nervous system (CNS) pathology that is primarily seen in the pediatric population. Ependymomas also exhibit a peak incidence in early childhood, with rare presentations after early adulthood. In this report, we describe a rare case of a 41-year-old male diagnosed sequentially with a polymorphous low-grade neuroepithelial tumor of the young followed by a supratentorial ependymoma within the span of a year. He underwent tumor resection for both tumors, as well as adjuvant radiation therapy for the ependymoma. Despite these interventions, he ultimately succumbed from tumor progression and post-operative complications. Currently, no genetic syndromes are known to link these two primary CNS tumors. Two commonalities at the chromosomal and cellular level include histone gene H3F3A mutations and positive Glial Fibrillary Acidic Protein staining on immunohistochemistry. To our knowledge, this unique dual pathology has not been previously described in the literature, making this case an avenue for further investigation and research into connections between these two distinct CNS pathologies.