SMAD5 and chronic myelogenous leukemia, BCR-ABL1 positive: Moreover, because it was previously shown that a blockade in the tumor-suppressing TGF-β signals could be involved in miR-155 oncogenic function (Rai et al., 2008[41]), we sought to measure the expression levels of two key members of the TGF-β pathway (TGF-βR2 and SMAD5) in CML and normal CD34+ cells.