SMAD4 and chronic myelogenous leukemia, BCR-ABL1 positive: In chronic myeloid leukaemia (CML), oncogenic BCR-ABL1 and the cellular ABL1 tyrosine kinase phosphorylate and inactivate SMAD4, thereby blocking the ability of SMAD4 to activate cell cycle protein-dependent kinase (CDK) inhibitor expression and induce cell cycle arrest.