Nanopore sequencing sheds a light on the FLT3 gene mutations complexity in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) patients carry in 27% of cases an activating mutation of the fms-like tyrosine kinase-3 (FLT3) gene: internal tandem duplication (ITD) or tyrosine kinase domain (TKD) point mutation. The simultaneous presence of both types of mutations, so-called FLT3 dual mutations, has been reported in 2% of APL, but this circumstance has never been studied. We studied a cohort of 74 APL cases, performing an in-depth analysis of three FLT3 dual mutant cases. Nanopore sequencing (NS) allowed us to characterize their complex mutational profile, showing the occurrence of multiple activating FLT3 mutations on different alleles in the leukemic promyelocytes and suggesting a cumulative impact of these events on the constitutive activation of the FLT3 pathway in APL cells. NS approach not only sheds light on the FLT3 mutational complexity in APL, but may also be useful to better clarify the FLT3 mutations landscape in acute myeloid leukemia.