CAL2 monoclonal antibody is a rapid and sensitive assay for the detection of calreticulin mutations in essential thrombocythemia patients
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Calreticulin (CALR) mutations are detected in the majority of JAK2 wild type patients with essential thrombocythemia (ET). Unlike JAK2V617F and MPL point mutations, CALR mutations are highly heterogeneous, with several types of indels being reported so far. CAL2 is a monoclonal antibody specifically recognizing the C-neoterminal peptide derived from all the frameshift mutations of CALR. We retrospectively analysed 172 ET patients diagnosed at our Institution from 1980 to 2015. In JAK2V617F- and MPLW515K/L-wild type patients CALR mutations were searched on peripheral blood and CAL2 immunostaining was performed on bone marrow. In addition, bone marrow biopsies were histologically reviewed for megakaryocytic features. Thirty-one patients (18%) were CALR-mutated. Concordance between molecular and immunohistological detection of CALR mutations was near complete, albeit a single patient was found to be positive by molecular tests only. Two patterns were defined in CAL2-positive bone marrow samples, characterized by staining of almost only megakaryocytes (pattern A: 41%) or staining of megakaryocytes and ≥ 2% small non megakaryocytic elements (pattern B: 59%), at least partially being myeloid precursors. Pattern B biopsies had higher cellularity and number of megakaryocytes compared to pattern A samples. In this series, CAL2 allowed rapid and cost-efficient identification of CALR-mutated ET patients. The biological significance of different staining pattern should be confirmed in wider and independent series.
KeywordsEssential thrombocythemia Calreticulin CAL2 Driver mutations Diagnostic tools
M.B. and M.C. designed the study; M.B., R.M. and L.S. treated patients, analysed the data and wrote the manuscript; A.P. and A.Z. performed histopathological tests and analysed the data; G.D.M., R.B. and C.C. performed molecular biology tests; G.L., G.P., A.S. and M.K. critically revised the manuscript. All authors have read and approved the final version.
Compliance with ethical standards
Conflict of interest
M. Bonifacio declares research funding from Novartis and received speaker bureau and advisory board honorarium from Amgen, Bristol-Myers Squibb, Incyte, Novartis and Pfizer, outside the present study. All the other authors declare no competing financial interests.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
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