Differential clinical effects of different mutation subtypes in CALR-mutant myeloproliferative neoplasms

Acute Lymphoblastic Leukemia Arising in CALR Mutated Essential Thrombocythemia

The development of acute lymphoblastic leukemia in an existing myeloproliferative neoplasm is rare with historical cases unable to differentiate between concomitant malignancies or leukemic transformation. Molecular studies of coexisting JAK2 V617F-positive myeloproliferative neoplasms and mature B cell malignancies indicate distinct disease entities arising in myeloid and lymphoid committed hematopoietic progenitor cells, respectively. Mutations of CALR in essential thrombocythemia appear to be associated with a distinct phenotype and a lower risk of thrombosis yet their impact on disease progression is less well defined. The as yet undescribed scenario of pro-B cell acute lymphoblastic leukemia arising in CALR mutated essential thrombocythemia is presented. Intensive treatment for the leukemia allowed for expansion of the original CALR mutated clone. Whether CALR mutations in myeloproliferative neoplasms predispose to the acquisition of additional malignancies, particularly lymphoproliferative disorders, is not yet known.

A link between the driver mutations and dysregulated apoptosis in BCR-ABL1 negative myeloproliferative neoplasms

The current understanding of BCR-ABL1 negative myeloproliferative neoplasms pathogenesis is centred on the phenotypic driver mutations in JAK2, MPL, or CALR genes, and the constitutive activation of JAK-STAT pathway. Nonetheless, there is still a need to better characterize the cellular processes that are triggered by these genetic alterations, such as apoptosis that might play a role in the pathological expansion of the myeloid lineages and, especially, in the morphological anomalies of the bone marrow megakaryocytes. In this article we will explore the connection between the driver mutations in MPN and the abnormal apoptosis that might be translated in new therapeutic strategies.

Molecular Pathogenesis and Clinical Significance of Driver Mutations in Primary Myelofibrosis: A Review

Primary myelofibrosis (PMF) is a rare chronic BCR-ABL1-negative myeloproliferative neoplasm characterized by progressive bone marrow fibrosis, inefficient hematopoiesis, and shortened survival. The clinical manifestations of PMF include splenomegaly, consequent to extramedullary hematopoiesis, pancytopenias, and an array of potentially debilitating constitutional symptoms. The diagnosis is based on bone marrow morphology and clinical criteria. Mutations in the JAK2 (V617F), MPL (W515), and CALR (exon 9 indel) genes are found in approximately 90% of patients whereas the remaining 10% are so-called triple negatives. Activation of the JAK/STAT pathway results in overproduction of abnormal megakaryocytes leading to bone marrow fibrosis. These mutations might be accompanied by other mutations, such as ASXL1. The commonly used prognostication scoring for PMF is based on the International Prognostic Scoring System. The subsequently developed Dynamic International Prognostic Scoring System-plus employs clinical as well as cytogenetic variables. In PMF, CALR mutation is associated with superior survival and ASXL1 with inferior outcome. Patients with triple-negative PMF have a higher incidence of leukemic transformation and lower overall survival compared with CALR- or JAK2-mutant patients. The impact of genetic lesions on survival is independent of current prognostic scoring systems. These observations indicate that driver and passenger mutations define distinct disease entities within PMF. Accounting for them is not only relevant to clinical decision-making, but should also be considered in designing clinical trials.