Among the different oncogenic kinase-driven neoplasia in which altered protein phosphorylation represents the molecular hallmark of the disease, the p210-BCR/ABL oncoproteins of the chronic myelogenous leukaemia (CML), can be considered the best example of an oncogene with constitutive tyrosine kinase activity (Calabretta and Perrotti, 2004). The gene discussed is ABL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.