- There is no limit to the number of prior treatment regimens. However, patients must have fully recovered from the acute toxic effects of all prior chemotherapy, immunotherapy, or radiotherapy prior to study enrollment. Acute toxicity of any previous therapy must have resolved to grade 1 or less, unless specified elsewhere. Myelosuppressive chemotherapy: Patients must not have received myelosuppressive chemotherapy within 3 weeks of enrollment (6 weeks if prior nitrosourea).