Here, we report a rare case of unclassified MPN (MPN-U) with a t(9;22)(p24;q11) leading to a 5′BCR/3′JAK2 fusion gene producing a fusion transcript that juxtaposed BCR exon 13 and JAK2 exon 17 and subsequently rapidly transformed into a myeloid granulocytic sarcoma. The gene discussed is JAK2; the disease is myeloproliferative neoplasm.