A t(8;9)(p22;p24)/PCM1-JAK2 Translocation in a Patient With Myeloproliferative Neoplasm and Myeloid Sarcoma: First Report in Korea

Dear Editor, Translocation t(8;9)(p22;p24) has been reported in diverse hematologic neoplasms, including acute leukemia, myeloproliferative neoplasm (MPN), and myelodysplastic syndromes/myeloproliferative neoplasm. These findings indicate that the mutation occurs in pluripotent, lymphoid-myeloid stem cells [1]. The pericentriolar material 1 (PCM1) gene, located on chromosome 8p22, encodes a protein with coiled-coil domains, and the Janus activated kinase 2 (JAK2) gene, located on chromosome 9p24, encodes non-receptor tyrosine kinases [2, 3]. The t(8;9) (p22;p24) leads to a PCM1-JAK2 fusion gene, resulting in the continuous activation of JAK2 tyrosine kinase [2]. Here we report a case of myeloid sarcoma (MS) and concurrent myeloproliferative neoplasm, unclassifiable (MPN, U), associated this translocation. A 42-yr-old man was referred to our hospital in April 2015 for left inguinal lymphadenopathy. He had visited another hospital 20 months earlier, in August 2013, owing to multiple cervical lymphadenopathies. At that time, complete blood count (CBC) revealed 10×10/L leukocytes, 9.9 g/dL hemoglobin, 166×10/L platelets, and peripheral blood (PB) smear demonstrated leukoerythroblastic reaction. Bone marrow (BM) biopsy showed both normal cellularity and a mixed pattern of fibrosis and normal cellularity. An abdominal computed tomography (CT) revealed splenomegaly. His neck lymph node (LN) was radically dissected and a pathologist interpreted the biopsy as showing metastatic malignancy of unknown origin. Based on this, the patient underwent neck radiotherapy and chemotherapy with 5-fluorouracil and cisplatin. After 13 months, in March 2015, a chest CT revealed enlarged LNs in the right axillary and an LN gun biopsy revealed MS. One week later, the patient developed left inguinal lymphadenopathy and was admitted to our hospital. A inguinal LN biopsy at our hospital also confirmed MS, and immunohistochemistry demonstrated positive results for myeloperoxidase and CD117 (Fig. 1A-C). CBC revealed 5.8×10/L leukocytes, 7.7 g/ dL hemoglobin, and 130 ×10/L platelets, and a PB smear showed leukoerythroblastic reaction (nucleated red blood cell [RBC]: 3/100 white blood cell [WBC]; metamyelocytes: 2%). BM aspiration indicated a normal myeloid:erythroid ratio and 3.2% eosinophils without myelodysplasia, and a biopsy confirmed hyperplasia and myelofibrosis without megakaryocytic proliferation and atypia (Fig. 1D-H). The patient tested negative for major/minor BCR-ABL1 rearrangement and JAK2, MPL, and