Study Assessing the Feasibility of a Surgery and Chemotherapy-Only in Children With Wnt Positive Medulloblastoma

Inclusion Criteria: * Participants must have classical histology posterior fossa medulloblastoma as determined by institutional neuro-pathological evaluation. * Sufficient pathologic material must be available for central analysis and review * Tumors will be deemed Wnt positive if, at the time of central analysis, there is: * Monosomy 6 as determined by array CGH * Gene transcript detection by NanoString supporting Wnt+ medulloblastoma * Absence of large-cell, anaplastic histology * Nuclear b-catenin IHC will be determined, but not required for the diagnosis * Absence of residual or disseminated disease as defined by the following criteria: Minimal residual disease as determined by post-operative imaging preferably performed within 48 hours of resection (and at most 28 days post-surgery), i.e. gross total resection or residual disease of \<1.5cm2 on post-operative imaging. No evidence of metastatic disease in the brain, spine or cerebral spinal fluid (CSF). Assessments must include MRI imaging of the brain and spine with and without contrast and a lumbar puncture for CSF cytology * Diagnostic imaging (pre and post contrast) must be forwarded to Dana-Farber Cancer Institute (DFCI) for central review to confirm eligibility * Patients must not have had any radiation therapy or chemotherapy for medulloblastoma prior to study enrollment * Patients must have a Lansky performance status of \>/=30 for children \</=10 years of age or a Karnofsky performance status of \> 30 for children \> 10 years of age. * Participants must have normal organ and marrow function as defined below: * Hemoglobin greater than 10 g/dL (can be transfused). Hemoglobin \<10 g/dL due to operative blood loss is permitted. * Absolute neutrophil count \> 1.0x109/L * Platelets \> 100,000/uL (non-transfused) * Total bilirubin \<1.5 x upper limit normal * SGOT (AST) or SGPT (ALT) \<2.5 x upper limit normal (ULN) for age * Creatinine clearance or radioisotope GFR \>70 ml/min/1.73m2 or normal serum creatinine for patient's age and gender * All females of child-bearing age must have a negative pregnancy test before being enrolled on study. All patients of child-bearing age must practice an effective method of birth control whilst undergoing chemotherapy on study. * No history of allergic reactions attributed to compounds of similar chemical or biologic composition to cisplatin, lomustine, vincristine or cyclophosphamide.