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Among these, gene rearrangements involving\n                    <jats:italic>PCM1::JAK2<\/jats:italic>\n                    are rare and may present diagnostic challenges, particularly when manifesting as acute lymphoblastic leukemia (ALL). We describe a case of a patient who presented with B-cell acute lymphoblastic leukemia (B-ALL) with a\n                    <jats:italic>JAK2<\/jats:italic>\n                    rearrangement. After the induction therapy, strong myeloid proliferation in bone marrow without evidence of residual lymphoblasts was observed and\n                    <jats:italic>JAK2<\/jats:italic>\n                    rearrangement was recognized to be a consequence of translocation t(8;9)(p22;p24)] resulting in\n                    <jats:italic>PCM1::JAK2<\/jats:italic>\n                    fusion. This finding indicated the presence of an underlying chronic myeloid\/lymphoid neoplasm, meeting criteria for MLN-eo-TK. Following an inadequate response to standard chemotherapy, salvage regimens incorporating targeted agents (JAK2 and BCL-2 inhibitors) and allogeneic bone marrow transplantation were administered, all of which unfortunately resulted in short-lived clinical benefit. The case highlights the importance of distinguishing de novo lymphoid malignancies from MLN-eo-TK, especially when\n                    <jats:italic>JAK2<\/jats:italic>\n                    rearrangements are detected. Recognition of the clonal myeloid component during or after lymphoid-directed therapy has important diagnostic and therapeutic implications, supporting the use of targeted JAK2 inhibition in addition to standard chemotherapy.\n                  <\/jats:p>","DOI":"10.1007\/s00277-026-06757-z","type":"journal-article","created":{"date-parts":[[2026,1,13]],"date-time":"2026-01-13T23:48:22Z","timestamp":1768348102000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["A case report and a literature review of Myeloid\/Lymphoid Neoplasm with Eosinophilia and PCM1::JAK2 rearrangement representing as B-cell acute lymphoblastic leukemia B-ALL"],"prefix":"10.1007","volume":"105","author":[{"given":"Luka","family":"\u010cema\u017ear","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Klara","family":"\u0160lajpah","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Njeto\u010dka","family":"Gredelj \u0160imec","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Helena","family":"Podgornik","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,1,14]]},"reference":[{"key":"6757_CR1","doi-asserted-by":"publisher","first-page":"2391","DOI":"10.1182\/blood-2016-03-643544","volume":"127","author":"DA Arber","year":"2016","unstructured":"Arber DA, Orazi A, Hasserjian R et al (2016) The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. 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