Recurrent Fusion of PCM1 to JAK2 in Atypical Chronic Myeloid Leukemia and Acute Leukemia Associated with the t(8;9)(p21-22;p23-24).

We have identified a novel, recurrent t(8;9)(p21–22;p23–24) in six patients with diverse hematological malignancies: atypical CML (n=4), secondary AML following idiopathic myelofibrosis (n=1) and pre B-ALL (n=1). Because of the involvement of several different tyrosine kinases in atypical CML, we focused our analysis on this class of gene. Initial FISH studies of one patient indicated that the janus kinase 2 gene (JAK2), located at 9p24, was disrupted. RACE-PCR was then used to identify the 8p21 partner gene as PCM1, a large centrosomal protein that contains multiple coiled-coil domains. RT-PCR and FISH analysis confirmed the fusion in this case, and also identified PCM1-JAK2 in the five other t(8;9) patients (RT-PCR and FISH, n=4; RT-PCR only, n=1; FISH only, n=1). Four different types of in-frame mRNA junction were identified, but in all cases the chimeric mRNA is predicted to encode a protein that retains several of the predicted coiled-coil domains from PCM1 and the entire tyrosine kinase domain of JAK2. Reciprocal JAK2-PCM1 mRNA could not be amplified in any patient. Clinically, 4 patients displayed CML-like hyperplasia with variable degrees of myelofibrosis and eosinophilia. Similar to typical CML, the clinical course of these patients was variable: one is alive 11 months after allogeneic stem cell transplantation, one transformed to acute leukemia 5 years after diagnosis, one died 4 days after presentation and one achieved a major cytogenetic response with interferon but died due to neurodegenerative disease and pneumonia at 7.5 years. Of the two remaining patients, one presented with secondary AML following idiopathic myelofibrosis and remains in remission 15 years after diagnosis following intensive chemotherapy and maintenance with interferon. The final patient died shortly after induction therapy for pre B-ALL. In conclusion, PCM1-JAK2 is a novel recurrent fusion gene in hematological malignancies that is likely to deregulate hemopoiesis in a manner similar to BCR-ABL. Patients with PCM1-JAK2 disease are attractive targets for signal transduction therapy.