Patients with tumors demonstrating positive PK, PD, and PG effects will continue treatment with ribociclib (21 days on, 7 days off) after surgery. This will constitute the Phase II component of the study. Patients will be treated until unacceptable toxicity is observed, or until disease progression as assessed by radiographic or clinical metrics. Preliminary rates of progression-free survival in patients with high-grade gliomas and high-grade meningiomas treated with ribociclib will be measured through radiographic and clinical response metrics, specifically Response Assessment in Neuro-Oncology (RANO) criteria and investigator discretion. Overall survival in patients with high-grade gliomas and high-grade meningiomas treated with ribociclib will be assessed by medical record review and survival follow up. Common Toxicity Criteria Adverse Event (CTC AE 4.0) will be utilized to review ribociclib treatment effects in patients with brain tumors. The trough plasma samples of ribociclib will be collected at pre-dosing on each clinical visit day (e.g., days 1, 22, 43, 64...) prior to the administration of ceritinib on that day. Ribociclib will be administered in the clinics on the clinic visit days to ensure the collection of trough level samples.