New agents in the treatment of childhood leukemias and myelodysplastic syndromes.

Relapsed or refractory leukemia remains the most common therapeutic problem in pediatric oncology. Particularly challenging is the patient who has recurrence following a stem cell transplant. Insights into the molecular pathogenesis of the leukemias have produced an array of new agents. These new agents will be more selective in hitting their targets, and so their use will be more narrowly defined than with classical cytotoxic drugs. These new agents include all-trans retinoic acid, gemtuzumab ozogamicin, imatinib mesylate, rituximab, and a bevy of signal transduction inhibitors and therapeutic monoclonal antibodies. Other new agents, such as liposomal daunorubicin, PEG-asparaginase, or clofarabine, represent chemical modifications of established antileukemic drugs. Increasingly, molecular profiling will be used to guide the development and application of new drugs.