Chronic myelogenous leukemia (CML) is a disease characterized by an initial chronic phase during which there is an abnormal proliferation of myeloid cell lineage. This treatable phase in general lasts 2-5 years, but without treatment it will inexorably progress to a final blast (or accelerated) phase for which there is no known treatment. The inappropriate expression of the EVI1 gene appears in the majority of CML patients. For a long time, the treatment of choice for CML was IFN-alpha, however recently a new drug, STI571, targets and inhibits the BCP/ABL activity in the leukemic cells. Because of increasing frequency of STI571 resistance, current NIH-sponsored clinical trials study a combination of STI571 and IFN-alpha in treatment of CML. The EVI1 gene is not detected in normal hematopoietic bone marrow but is expressed in about 30% to 80% of CML patients. We showed that EVI1 is an aggressive oncogene. New advances in our work indicate that EVI1 abrogates the effects of IFN-alpha in vitro, that IFN-alpha-resistant chronic phase CML patients express EVI1, and that the forced expression of EVI1 in IFN-alpha hematopoietic cell lines abrogates the growth-inhibitory response to IFN-alpha. Taken together, these data provide the first clear correlation between a CML-associated gene and the failure to respond to IFN-alpha inhibition. Based on the background presented, we propose that CML patients who inappropriately express EVI1 will not respond to IFN-alpha therapy alone or in combination with STI571. It is also possible that the EVI1-positive patients treated with STI571 and IFN-alpha could actually be harmed because treatment with IFN-alone will preclude the use of the alternative drug Cytarabine also used in clinical trials in combination with STI571. The goal of this proposal is to design a sensitive routine test to identify CML patients who express EVI1 and who therefore will not benefit from IFN-alpha therapy. The goals are: First, we will define the best experimental conditions for quantification of the expression of EVI1 in leukemia and control samples. Second, we will determine whether EVI1 expression in chronic phase patients induces a faster progression of the disease to the blast phase. Real-time RT-PCR analysis and statistical analysis of CML and control samples will be used for this study.