A Study of PD 0332991 in Patients With Recurrent Rb Positive Glioblastoma

Inclusion Criteria: * Patients 18 years or older with KPS \> 60, with life expectancy of \> 8 weeks with radiographically proven recurrent, intracranial Glioblastoma multiforme or Gliosarcoma; patients must have documentation of Rb positive disease. * All patients must sign an informed consent and must have signed an authorization for the release of their protected health information. * Patients must have had prior external beam radiation and temozolomide chemotherapy; there is no limit to the number of prior chemotherapies used; patients may be treated in their first, second or third relapse * Patients must have recovered from the toxic effects of prior therapy * Patients must have adequate bone marrow function and renal function before starting therapy. A pre-study EKG with a normal QT interval is required for all patients * Patients must have shown unequivocal evidence for tumor progression by MRI scan and on a steroid dose that has been stable for at least 7 days. * Patients must have an interval of greater than or equal to 42 days from the completion of radiation therapy to study entry. * A subset of 15 patients will be enrolled prior to a planned, indicated surgical resection. Patients can be enrolled pre-operatively only if they are surgical candidates, do not have evidence of an acute intracranial hemorrhage and are able to start protocol treatment in a window of 7 days before surgery. * Male and female patients with reproductive potential must use an approved contraceptive method. Women of childbearing potential must have a negative beta-HCG pregnancy test * Blocks or slides of tumor tissue from a previous surgery must be available to do IHC Rb staining. Patients with negative tumors (Rb negative) will be excluded from the study. Exclusion Criteria: * Patients must not have any significant medical illnesses that in the investigator's opinion cannot be adequately controlled with appropriate therapy or would compromise the patient's ability to tolerate this therapy. * Patients with a history of any other cancer (except non-melanoma skin cancer or carcinoma in-situ of the cervix), unless in complete remission and off of all therapy for that disease for a minimum of 3 years are ineligible. * Patients on enzyme-inducing anti-epileptic drugs or other drugs that cause CYP3A enzyme induction or inhibition will not be eligible