Interestingly, we observed an opposite growth of BCR::ABL1 and JAK2 under TKI treatment, with BCR::ABL1 decrease and JAK2 increase in the majority of patients of our systematic review (81.8% in concomitant CML and Ph-negative MPN; 65% in CML preceding Ph-negative MPN; 41.86% in MPN preceding CML). Here, BCR is linked to chronic myelogenous leukemia, BCR-ABL1 positive.