Tehran University of Medical Sciences International Journal of Hematology-Oncology and Stem Cell Research 2008-2207 15 4 2021 10 14 255 259 EN Ayesha Butt Aga Khan University Hospital, Karachi, Pakistan Rhul Quddus Aga Khan University Hospital, Karachi, Pakistan Natasha Ali Aga Khan University Hospital, Karachi, Pakistan 2020 05 14 2020 06 13 A-64-year old male presented with cough, weight loss, and maculopapular rash for 15-20 days. On examination, he was found to have cervical lymphadenopathy and splenomegaly. His leukocyte count was 62.1x109/L, platelets were 1169x109/L and LDH was 816 IU/L. Peripheral blood film showed a leukoerythroblastic picture with thrombocytosis. He was started on hydroxyurea and allopurinol. Subsequently, bone marrow evaluation was done which depicted increased lymphoid cells with an M:E ratio of 4:1. Cellular areas exhibited an increase in myeloid precursors along with prominent lymphoid cells and abundant megakaryocytes. Immunohistochemistry showed an increase in B-lymphocytes. Grade MF-2 reticulin fibrosis was noted. Overall findings suggested essential thrombocythemia (ET). On flow cytometry, CD45-positive lymphoid cells population was 31% and showed reactivity to Pan-B-markers with lambda light chain restriction. Janus Kinase (JAK) 2 mutation was detected while BCR-ABL1 translocation was negative. A diagnosis of ET progressing to myelofibrosis and mature B-lymphoproliferative disorder was made. Hydroxyurea and allopurinol were stopped while ruxolitinib was introduced and 2.5 years later he remains stable on this treatment. https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/view/1338 https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/download/1338/892