The purpose of this study is to determine the safety and tolerability of an oral Farnesyl Protein Transferase Inhibitor (SCH 66336) as a single agent in patients with Advanced Myelodysplastic Syndrome, Acute Myelogenous Leukemia, Chronic Myelogenous Leukemia in Blast Crisis, or Acute Lymphoblastic Leukemia.

Inclusion Criteria:

• Pathologically documented chronic myelogenous leukemia in blast crisis, myelodysplasia, acute myelogenous leukemia, or acute lymphocytic leukemia.
• Life expectancy of 12 weeks or greater.
• ECOG Performance Status less than or equal to 2.
• Meets protocol requirements for specified laboratory values.
• No manifestations of a malabsorption syndrome.

Exclusion Criteria:

• Patients who have received more than three chemotherapy regimens for more than three recurrences of the disease.
• Poor medical risks because of nonmalignant systemic disease as well as those with active uncontrolled conditions.
• Patients who have received investigational therapy of any type within 30 days prior to administration.