PCM1-JAK2 fusion mutations are rare variants that activate a tyrosine kinase leading to a variety of neoplasms that can involve any hematologic cell line. They most often present as myelodysplasia (MPD) and can demonstrate prominent eosinophilia and/or erythrodysplasia. Transformation to acute leukemia is often seen, as is de novo leukemia. Lymphomas have also been reported. The diagnosis can often be made with routine cytogenetic analysis but specific probes and detailed next generation sequencing may be necessary. JAK2 inhibitors are active in MPD as is stem cell transplantation. Transplantation has occasionally been successful in leukemic phase as well. The current case highlights both the difficulties in diagnosis as well as the second successful treatment of MPD, transformed into acute lymphoblastic leukemia.
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