Immune Checkpoint Inhibitor Nivolumab in People With Recurrent Select Rare CNS Cancers

Background: More than 130 primary tumors of the central nervous system (CNS) have been identified. Most affect less than 1,000 people in the United States each year. Because these tumors are so rare, there are few proven therapies. This study will test whether the immunotherapy drug nivolumab is an effective treatment for people with rare CNS tumors. Objectives: To learn if stimulating the immune system using the drug nivolumab can shrink tumors in people with rare CNS (brain or spine) tumors or increase the time it takes for these tumors to grow or spread. Eligibility: Adults whose rare CNS tumor has returned. Design: Individuals will be screened: * Heart and blood tests * Physical and neurological exam * Hepatitis tests * Pregnancy test * Magnetic resonance imaging (MRI). They will lay in a machine that takes pictures. * Tumor tissue sample. This can be from a previous procedure. At the start of the study, participants will have blood tests. They will answer questions about their symptoms and their quality of life. Individuals will get nivolumab in a vein every 2 weeks for up to 64 weeks. Individuals will have monthly blood tests. Every other month they will have an MRI and a neurologic function test. They will also answer questions about their quality of life. Genetic tests will be done on individuals' tumor tissue. Individuals will be contacted if any clinically important results are found. After treatment ends, individuals will be monitored for up to 5 years. They will have a series of MRIs and neurological function tests. They will be asked to report any symptoms they experience....

* INCLUSION CRITERIA: * Histopathologically proven diagnosis of Ependymoma, Medulloblastoma, Parenchymal Pineal Region Tumors (Pineoblastoma, Pineocytoma, Pineal Tumor of Intermediate Differentiation, Papillary Tumor of the Pineal Region), Choroid Plexus Tumors (Carcinoma, Papilloma, Atypical Papilloma), Histone Mutated Gliomas, Gliomatosis Cerebri, Atypical Teratoid/Rhabdoid Tumor (ATRT), Malignant/Atypical Meningioma\*, Gliosarcoma or Primary CNS Sarcoma, Pleomorphic Xanthoastrocytoma (PXA) and Anaplastic Pleomorphic Xanthoastrocytoma (APXA), and tumors formerly known as Primitive Neuro-Ectodermal Tumors (Embryonal Tumor with Multilayered Rosettes, Medulloepithelioma, Central Nervous System (CNS) Neuroblastoma, CNS Ganglioneuroblastoma, CNS Embryonal Tumor NOS; and tumor entities emerging from methylation profiling of CNS-PNETs: CNS neuroblastoma with Forkhead box protein R2 (FOXR2) activation, CNS Ewing sarcoma family tumor with CIC alteration, CNS high-grade neuroepithelial tumor with meningioma 1 (MN1) alterations, and CNS high-grade neuroepithelial tumor with BCOR alteration) prior to registration. \*Individuals with extra CNS metastases from meningioma will be eligible even if pathology review fails to demonstrate high grade features on available tumor samples. * The tumor tissue (e.g., block or 20 unstained slides) must be available to be sent for immunophenotyping by National Cancer Institute (NCI) Laboratory of Pathology. * Individuals must have progressive tumor growth after having received established standard of care and/or other experimental treatments for their newly diagnosed or recurrent disease. Individuals will be enrolled into 2 different cohorts (cohort 1 or heavily pretreated; cohort 2 or not heavily pretreated). * Age \>= 18 * Karnofsky performance status \>= 70 within 14 days prior to Step 2 registration; Individuals with severe paraparesis/paraplegia who need minimal assistance for selfcare due to their motor deficit but are otherwise functionally independent will be considered eligible. * Adequate hematologic function based on complete blood count (CBC)/differential within 14 days prior to Step 2 registration defined as follows: * Absolute neutrophil count \>= 1,500 cells/mm\^3; * Platelet count \>= 100,000 cells/mm\^3 * Hemoglobin \> 9.0 g/dl (may be transfused to achieve this level) * Adequate renal function within 14 days prior to Step 2 registration defined as follows: * Blood urea nitrogen (BUN) \