SRP414289 PRJNA911024 Single cell analysis of leukemic transformation in Myeloproliferative Neoplasms Myeloproliferative neoplasms (MPN) are clonal disorders of hematopoietic stem cells that include polycythemia vera, essential thrombocythemia, and primary myelofibrosis. 10-20% of MPN pts transform to secondary acute myeloid leukemia (sAML), unresponsive to conventional therapy and associated with dismal outcome (Dunbar A, 2020). In addition to somatic driver mutations affecting JAK2, CALR or MPL, several additional variants are harbored by MPN pts inb chronic phase, and a restricted set of them were associated with risk of leukemic evolution (Vannucchi AM, Leukemia 2013; Tefferi A, Blood ASdv 2016) However, the molecular mechanisms underlying leukemic transformation remain largely unknown. Although bulk next generation sequencing (NGS) highlights the overall mutation landscape, it cannot distinguish which mutations occur in the same clone(s), nor elucidate the order of mutations or resolve clonal complexity. Conversely, single-cell sequencing (SCS) might allow to resolve clonal heterogeneity and reconstruct clonal phylogenies at each disease phase (Parenti, NPJ Prec Onc 2021)).To delineate the clonal landscape of sAML, we performed single-cell mutational profiling in 10 pts with MPNs who progressed to sAML.