Impact of FLT3-ITD allele ratio and ITD length on therapeutic outcome in cytogenetically normal AML patients without NPM1 mutation

Mutations of internal tandem duplication in FMS-like tyrosine kinase 3 (FLT3-ITD) contribute to poor prognosis in cytogenetically normal acute myeloid leukemia (CN-AML). Chemotherapy has limited effect, while allogeneic hematopoietic stem cell transplantation (allo-HSCT) plus sorafenib maintenance is a promising protocol to improve their therapeutic outcome. However, the prognostic significance of FLT3-ITD mutant status remains controversial. To investigate this, we detected FLT3-ITD mutant ratio (high and low) and length (long and short) in enrolled 184 CN-AML patients without NPM1 mutation, and evaluated their impact on complete remission (CR), overall survival (OS), relapse-free survival (RFS) and relapse risk (RR) after chemotherapy or allo-HSCT plus sorafenib maintenance. Our studies showed that FLT3-ITD mutation had negative impact on chemotherapeutic response, OS and RFS in CN-AML patients. There was no significant difference in CR rate between high and low ratio, or long and short length. Increasing ITD mutant ratio and length were associated with decreasing OS, and long length had shorter RFS and higher RR than the short after chemotherapy. Allo-HSCT plus sorafenib maintenance was an effective strategy to improve RFS and decrease relapse probability in FLT3-ITD AML patients, and benefited to these regardless of mutant ratio, and those with long length instead of the short.