Increased coexpression of <i>c-KIT</i> and <i>FLT3</i> receptors on myeloblasts: Independent predictor of poor outcome in pediatric acute myeloid leukemia

Background: Significance of mutations in <i>FLT3</i> and <i>c-KIT</i> genes in AML has been well established, but role of their coexpression has not been evaluated. The aim of this study was to evaluate clinical significance of <i>FLT3</i> (CD135) and <i>c-KIT</i> (CD117) coexpression on myeloblasts in AML. Methods: Using flow-cytometry, we prospectively observed in 115 AML patients that CD135, CD117, and CD135+CD117 coexpression was expressed in 95 (82%), 104 (90%), and 81 (70%) patients respectively. Median expression of CD135, CD117, and their co expression was used as cut off for high and low expression. Results: <i>FLT3</i> ITD (internal tandem duplication) was present in 20 (17%) patients. High coexpression did not correlate with <i>FLT3</i> ITD (P = 0.432) and cytogenetics (P = 0.244). Out of 115 patients, 86 (74.7%) achieved remission. At median followup of 15.5 months, EFS and OS was 29% and 35%, respectively for the entire cohort. Patients with high coexpression of CD135 and CD117 in comparison to those with low coexpression had significantly inferior EFS (20% vs 38% P &#60; 0.001) and OS (27% vs 44% P = 0.001). In step wise Cox regression multivariable analysis, hazard ratio for high hemoglobin, WBC count, and coexpression of CD135 and CD117 was 0.63, 1.73, and 2.46 respectively for EFS, and for OS only CD135+CD117 coexpression emerged as an independent predictor (hazard ratio 2.25). Conclusions: This is the first study to show that high coexpression of CD135+CD117 is an independent predictor of poor outcome in AML and is easily measurable by routine diagnostic flow-cytometry