- Patients must have recovered from the toxic effects of prior therapy (including resolution of effects on laboratory values): 2 weeks from any investigational agent, 4 weeks from prior cytotoxic therapy, 2 weeks from vincristine, 6 weeks from nitrosoureas, 3 weeks from procarbazine administration, and 1 week for non-cytotoxic agents e.g. tamoxifen, cis- retinoic acid, etc. (radiosensitizer does not count). Any questions related to the definition of non-cytotoxic agents should be directed to the PI.