Background: Mutations in the receptor tyrosine kinase (RTK) Fms-like tyrosine kinase 3 (FLT3) gene are among the most common somatic mutations in AML with FLT3 internal tandem duplications (ITDs) occurring in 20-35% of adult and 5-15% of pediatric AML. While the presence of FLT3ITD mutation does not appear to influence outcome to induction chemotherapy, this mutation has been shown to confer a poor prognosis with significantly shorter disease free and relapse free survival. For patients with intermediate risk cytogenetically normal AML, molecular testing for FLT3-ITD has recently been incorporated into the National Comprehensive Cancer Network (NCCN) guidelines for clinical practice. However, while molecular testing can identify a subset of patients at high risk for relapse, there remains clinical heterogeneity likely due to differences in activation of signal transduction networks. Methods: Modulated SCNP was performed sequentially on two independent sets of patient samples (n=32 peripheral blood and n=85 bone marrow samples respectively). 304 and 201 “node-metric” i.e. modulated read outs of dynamic elements on individual proteins in signaling pathways were measured in the two sets respectively. These were derived from pathways known to be relevant to Flt3-WT and Flt3-ITD signaling (e.g. Ras-Raf-Erk-S6, PI3K-Akt-S6, STATs), as well as in-vitro chemotherapeutic induction of apoptosis (cleaved PARP, cleaved caspases), phosphatases, drug transporters (e.g. MDR-1, ABCG2) and expression of growth factor RTKs (e.g. Flt3R, c-Kit). FIGURE 1. PATHWAYS ASSESSED USING SCNP ASSAY FIGURE 4. Flt3-ITD “OUTLIER” SAMPLE SIGNALS LIKE Flt3-WT FIGURE 2. PATIENT AND SAMPLE CHARACTERISTICS FIGURE 3. ASSOCIATION OF ASSAY READ-OUTS WITH FLT3 STATUS