- Patients who have had chemotherapy or radiotherapy within 4 weeks (6 weeks for nitrosoureas or mitomycin C) prior to beginning treatment or those who have not recovered from treatment-limiting adverse events (to grade 1 or better) due to agents administered more than 4 weeks earlier. At least 4 weeks must have elapsed since any major surgery prior to study enrollment. Continuous use of supportive care medications (i. e. growth factors, anagrelide, or hydroxyurea) is allowed.