- Patients must have been off chemotherapy for 2 weeks prior to entering this study and recovered from the toxic effects of that therapy; use of hydroxyurea on patients with rapidly proliferative disease (i.e., absolute peripheral blood blast count >= 5 x 10^9/L, and increasing by >= 1 x 10^9/L/24 hrs) is allowed up to 24 hours prior to the start of therapy with PS-341