To evaluate the mechanistic link between ruxolitinib exposure and RAS pathway mutations selection, we next investigated whether ruxolitinib positively selects RAS mutant clones through ex vivo treatment of primary human CD34+ hematopoietic cells sorted from peripheral blood mononuclear cells of patients with RAS-mutated MPN (n = 6). This evidence concerns the gene CD34 and myeloproliferative neoplasm.