Inclusion criteria:

          -  Written informed consent must be obtained prior to any screening procedures

          -  Patients age 18-85 are eligible for study participation

          -  History of grade III or IV glioma (GBM or AG) with archived FFPE and/or frozen tumor
             tissue available

          -  Patient must be a candidate for surgical resection of recurrent high-grade glioma

          -  Karnofsky Performance Scale score ≥ 70.

          -  Life expectancy of 4 months or longer.

          -  Received at least 1 prior systemic therapy for glioma.

          -  A sufficient interval must have elapsed between the last dose of prior anti-cancer
             therapy (including cytotoxic and biological therapies and major surgery) and
             enrollment, to allow the effects of prior therapy to have abated

          -  Patients must have adequate organ function

          -  For continued ribociclib treatment after surgery, immunohistochemical (IHC)
             confirmation of Rb expression in ≥50% of malignant tumors cells in at least 1 tumor
             specimen is

        Exclusion criteria:

          -  Impairment of gastro-intestinal (GI) function or GI disease that may significantly
             alter the absorption of ribociclib such as patients with a history of GI surgery which
             may result in intestinal blind loops and patients with clinically significant
             gastroparesis, unresolved nausea, vomiting, or diarrhea of CTCAE grade > 1

          -  Impaired cardiac function or clinically significant cardiac diseases

          -  Patients who are currently receiving treatment (within 5 days prior to starting study
             drug) with agents that are metabolized predominantly through CYP3A4 and that have a
             narrow therapeutic window. Agents including vitamins, supplements, and herbal
             supplements that are either (i) metabolized solely through CYP3A4/5, CYP1A2 or BSEP
             and have a narrow therapeutic window or (ii) are strong inhibitors of CYP3A4/5, CYP1A2
             or BSEP. Agents that are known strong inducers or inhibitors CYP3A4 are prohibited.
             Patients must avoid consumption of grapefruit, Seville oranges or products containing
             the juice of each during the entire study and for 7 days before the first dose.

          -  Patients with concurrent severe and/or uncontrolled concurrent medical conditions that
             the investigator believes could compromise participation in the study (e.g.,
             uncontrolled hypertension and/or diabetes mellitus, clinically significant pulmonary
             disease, clinically significant neurological disorder, active or uncontrolled
             infection)

          -  Pregnant or lactating women, where pregnancy is defined as the state of a female after
             conception and until the termination of gestation, confirmed by a positive hCG
             laboratory test (> 5 mIU/mL).

          -  Women of childbearing potential, defined as all women physically capable of becoming
             pregnant, unless they are using effective methods of contraception during dosing of
             study treatment. Effective contraception must be used by both sexes (female patients
             and their male partners) during study treatment and for 30 days after the last dose of
             study medication

          -  Fertile males must be willing to use contraception. Fertile males must use condom with
             spermicide (double barrier method). Effective contraception, as defined above, must be
             used by both sexes (male patients and their female partners) during study treatment
             and for 30 days after the last dose of study medication. A condom is required to be
             used by vasectomized men in order to prevent delivery of the study drug via seminal
             fluid.

          -  Patients unwilling or unable to comply with the protocol

          -  Known diagnosis of human immunodeficiency virus (HIV) or hepatitis C (testing is not
             mandatory)