BCR and chronic myelogenous leukemia, BCR-ABL1 positive: Some Ph-negative MPNs, particularly ET, have been detected to have very low level of BCR::ABL1 transcripts of no clinical and pathologic significance (38) and likewise, the presence of JAK2 mutation, usually at low allelic burden, in the context of a CML may not change the clinical features of CML (58, 59).