- Patients must have been off chemotherapy for the 4 weeks prior to entering this study and recovered from the toxic effects of that therapy; patients with evidence of rapidly progressive disease (i.e., absolute peripheral blood blast count >= 5 x 10^9/L and increasing by >= 1 x 10^9/L/24 hours) may receive treatment before 4 weeks from the previous treatment providing they have recovered from all toxic effects of that therapy; use of hydroxyurea on patients with rapidly proliferative disease is allowed up to 24 hours prior to the start of therapy