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Introduction: The mechanism of relapsed CD19(−) B‐ALL after anti‐CD19 immunotherapy (Kymriah [CART‐19] and blinatumomab) is under active investigation. Our study aims to assess LILRB1 as a novel B‐cell marker for detecting CD19(−) B‐lymphoblasts and to analyze the clinicopathologic/genetic features of such disease to provide biological insight into relapse. Methods: Six patients (3 males/3 females, median age of 14 years) with relapsed CD19(−) B‐ALL were analyzed for cytogenetic/genetic profile and immunophenotype. Results: CD19(−) B‐ALL emerged after an interval of 5.8 months following anti‐CD19 therapy. Five of six patients had B‐cell aplasia, indicative of a persistent effect of CART or blinatumomab at relapse. Importantly, LILRB1 was variably expressed on CD19(−) and CD19(+) B lymphoblasts, strong on CD34(+) lymphoblasts and dim/partial on CD34(−) lymphoblasts. Three of six patients with paired B‐ALL samples (pre‐ and post‐anti‐CD19 therapy) carried complex and different cytogenetic abnormalities, either as completely different or sharing a subset of cytogenetic abnormalities. Conclusion: LILRB1 can be used as a novel B‐cell marker to identify CD19(−) B lymphoblasts. The emergence of CD19(−) B‐ALL appears to be associated with complex cytogenetic evolutions. The mechanism of CD19(−) B‐ALL relapse under anti‐CD19 immune pressure remains to be explored by comprehensive molecular studies. [ABSTRACT FROM AUTHOR]

Philadelphia (BCR- ABL)- negative myeloproliferative neoplasms (MPNs) include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). MPN can transform into an accelerated or a blast phase, which is associated with poor response to standard therapy and low overall median survival. We present an interesting case of a patient with a history of PMF and progression and summarize the current studies on genetic features of myeloproliferative neoplasms in blast phase (MPN- BP) with an emphasis on PMF. Although MPN- BP show ≥20% blasts in peripheral blood or bone marrow, it is not considered as acute myeloid leukemia (AML) according to the WHO classification. While MPNs- BP typically lack genetic mutations seen in de novo AML, they commonly harbor IDH1/2, SRSF2, ASXL1, and TP53 mutations, similar to the genetic profiles of acute myeloid leukemia with myelodysplasia-related changes (AML- MRC). [ABSTRACT FROM AUTHOR]

Philadelphia (BCR‐ABL)‐negative myeloproliferative neoplasms (MPNs) include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). MPN can transform into an accelerated or a blast phase, which is associated with poor response to standard therapy and low overall median survival. We present an interesting case of a patient with a history of PMF and progression and summarize the current studies on genetic features of myeloproliferative neoplasms in blast phase (MPN‐BP) with an emphasis on PMF. Although MPN‐BP show ≥20% blasts in peripheral blood or bone marrow, it is not considered as acute myeloid leukemia (AML) according to the WHO classification. While MPNs‐BP typically lack genetic mutations seen in de novo AML, they commonly harbor IDH1/2, SRSF2, ASXL1, and TP53 mutations, similar to the genetic profiles of acute myeloid leukemia with myelodysplasia‐related changes (AML‐MRC). [ABSTRACT FROM AUTHOR]

Introduction: Myeloperoxidase (MPO) is considered a specific marker of myeloid/non‐monocytic lineage in the diagnosis of mixed phenotype acute leukemia (MPAL). However, the clinical significance of isolated dim MPO expression in otherwise typical B lymphoblastic leukemia (B‐ALL; referred to as B/myeloid MPALisoMPO) in adult patients is unknown. Methods: We compared flow cytometric immunophenotype and clinicopathological findings among cases of B/myeloid MPALisoMPO (n = 13), other MPAL subtypes (n = 10, B/myeloid and T/myeloid MPAL), B‐ALL (n = 64), and acute myeloid leukemia (AML, n = 58), using the 2016 WHO classification. For MPAL cases, MPO was reported as the percent of MPO positive blasts and its intensity (dim or moderate/strong). The pattern of heterogenous antigen expression (inversely coordinated expression between myeloid and lymphoid markers and cell size) was assessed. Results: Cases of B/myeloid MPALisoMPO showed a fairly homogenous single B‐lineage blast population with dim MPO expression whereas cases of other MPAL subtypes displayed heterogeneous antigen expression and moderate/strong MPO expression. The percent of MPO positive blasts in these two groups was similar. Expressions of CD15, CD117, and monocytic markers were more common in other MPAL than in B/myeloid MPALisoMPO. B/myeloid MPALisoMPO patients had similar overall and leukemia free survivals as B‐ALL patients and better than other MPAL patients. Conclusion: This is the first study to investigate the clinical significance of adult B/myeloid MPALisoMPO using the 2016 WHO classification. Our results suggest that B/myeloid MPALisoMPO clinically behaves more similarly to B‐ALL than to other MPAL subtypes, supporting the 2016 WHO classification to segregate this entity from other MPAL subtypes. [ABSTRACT FROM AUTHOR]