<qa>  What is the hematologic toxicity of AC220?Several FLT3 inhibitors have been evaluated or are currently being tested in the setting of relapsing AML. In most trials to date, patients were only eligible if the FLT3-ITD mutation was present. Disappointing results were reported with the first generation of FLT3 inhibitors, including lestaurtinib CEP-701, midostaurin PKC-412 and sorafenib. Second generation FLT3 inhibitors such as quizartinib AC220 are currently under investigation with promising results. However, the hematologic toxicity of AC220 will likely present a major limitation in evaluating AC220 combined with standard or high-dose chemotherapy. 