The mainstay of therapy for the myeloproliferative neoplasms (MPN) has been phlebotomy, antiplatelet drugs and cytoreductive agents to control constitutional symptoms and to prevent leukemic transformation and thrombotic events. There exists an increased incidence of both arterial and venous thrombosis in MPN patients, of which the latter may manifest in the microcirculation or as deep vein thrombosis, pulmonary embolism, cerebral venous thrombosis or splanchnic vein thrombosis (SVT). SVT can be the first presenting feature of either a hematologically evident or latent MPN with the molecular identification of the JAK2 V617F MPN driver mutation an essential component of the molecular diagnostic work up in such cases in order to assign appropriate clinical management.[2, 3] Subsequently identified low frequency MPN-driving mutations in JAK2 exon 12 and MPL exon 10 are generally considered to be absent in SVT,[4, 5] although rare case reports exist.[6, 7] The landmark discovery in 2013 of insertion and/or deletion (indel) mutations of CALR (the gene that encodes the endoplasmic reticulum-associated, calcium binding protein Calreticulin) in up to 80% of JAK2 V617F-negative essential thrombocythemia and primary myelofibrosis patients[8, 9] prompted several groups to investigate whether these mutations were also prevalent in patients presenting with SVT, enabling a prompt diagnosis of MPN.
To date, multiple studies have reported the incidence of CALR mutations in patient cohorts presenting with SVT and are summarized in Table 1.[10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23] Of more than 1500 SVT patients now analyzed, CALR mutations were present in only 1.3% of patients, roughly equating to one patient in seventy-five. Screening all SVT patients for CALR mutations would therefore appear to be an inappropriate use of resources; however, this issue has been recently addressed. Incorporating a spleen size of greater than 16 cm and a platelet count of more than 200 × 109/L into the diagnostic algorithm allows for the positive identification of the majority of CALR mutation-positive cases, sparing the remainder of patients from an invasive bone marrow biopsy required to assess morphological appearances. As marked geographical differences exist in the etiology of SVT and Budd-Chiari syndrome, [24, 25] the above algorithm requires verification in regional-specific cohorts.
Studies reporting the incidence of CALR mutations in patients with splanchnic vein thrombosis.
|Reference No.||SVT patients (n)||CALR+||SVT site||MPN diagnosis|
|||209||4 (1.9%)||BCS (n = 2), PVT (n = 2)||ET (n = 3), PMF (n = 1)|
|||66||1 (1.5%)||Not specified||Not specified|
|||83||2 (2.4%)||PVT (n = 2)||ET (n = 1), MPN-U (n = 1)|
|||41||2 (4.9%)||BCS (n = 2)||ET (n = 1), PMF (n = 1)|
|||312∗||5 (1.6%)||BCS (n = 1), PVT (n = 4)||ET (n = 1), PMF (n = 4)|
|||210||2 (1.0%)||BCS (n = 2)||Not specified|
|||24||2 (8.3%)||BCS (n = 2)||Not specified|
From a laboratory perspective, a further two issues require consideration. Some recent evidence suggests that MPN patients with SVT have a significantly lower JAK2 V617F allele burden (< 10%) than those MPN patients without SVT. Whether this phenomenon is also observed in patients with CALR+ SVT remains to be answered. Given the number of methodological approaches available for the detection of CALR mutations,[27, 28] careful validation and selection of a sensitive technique is required so as not to underdiagnose the potential underlying MPN. Secondly, all the pathologically annotated, MPN-associated CALR indel mutations result in a +1 alteration of the reading frame leading to a loss of the terminal calreticulin localization domain. CALR mutations in two SVT patients have been reported as being in-frame[19, 21]: caution in interpretation is required as these mutations may be of germ-line origin and of uncertain pathogenicity. Sequencing of CALR in patient constitutional material is consequently needed for clarification.
Screening for CALR mutations in SVT patients remains a worthwhile endeavor as diagnosis of the underlying MPN is critical for fitting patient treatment. Future work on CALR mutation type and allele burden may reveal insights into the pathogenetic mechanisms at play in patients with SVT.
Smalberg JH Arends LR Valla DC Kiladjian JJ Janssen HL Leebeek FW. Myeloproliferative neoplasms in Budd-Chiari syndrome and portal vein thrombosis: a meta-analysis. Blood 2012; 120:4921-8.
De Stefano V Qi X Betti S Rossi E. Splanchnic vein thrombosis and myeloproliferative neoplasms: molecular-driven diagnosis and long-term treatment. Thromb Haemost 2016; 115:240-9.
Kiladjian JJ Cervantes F Leebeek F Marzac C Cassinat B Chevret S et al. The impact of JAK2 and MPL mutations on diagnosis and prognosis of splanchnic vein thrombosis: a report on 241 cases. Blood 2008; 111: 4922-9.
Fiorini A Chiusolo P Rossi E Za T De Ritis DG Ciminello A et al. Absence of the JAK2 exon 12 mutations in patients with splanchnic vein thrombosis and without overt myeloproliferative neoplasms. Am J Hematol 2009; 84: 126-7.
Colaizzo D Amitrano L Tiscia GL Grandone E Guardascione MA Margaglione M. A new JAK2 gene mutation in patients with polycythemia vera and splanchnic vein thrombosis. Blood 2007; 110:2768-9.
Bergamaschi GM Primignani M Barosi G Fabris FM Villani L Reati R et al. MPL and JAK2 exon 12 mutations in patients with the Budd-Chiari syndrome or extrahepatic portal vein obstruction. Blood 2008; 111:4418.
Klampfl T Gisslinger H Harutyunyan AS Nivarthi H Rumi E Milosevic JD et al. Somatic mutations of calreticulin in myeloproliferative neoplasms. N Engl J Med 2013; 369:2379-90.
Nangalia J Massie CE Baxter EJ Nice FL Gundem G Wedge DC et al. Somatic CALR mutations in myeloproliferative neoplasms with nonmutated JAK2. N Engl J Med 2013; 369:2391-405.
Turon F Cervantes F Colomer D Baiges A Hernández-Gea V Garcia-Pagán JC. Role of calreticulin mutations in the aetiological diagnosis of splanchnic vein thrombosis. J Hepatol 2015; 62:72-4.
Haslam K Langabeer SE. Incidence of CALR mutations in patients with splanchnic vein thrombosis. Br J Haematol 2015; 168:459-60.
Iurlo A Cattaneo D Gianelli U Fermo E Augello C Cortelazzi A. Molecular analyses in the diagnosis of myeloproliferative neoplasm-related splanchnic vein thrombosis. Ann Hematol 2015; 94:881-2.
Rocques M Park JH Minello A Bastie JN Girodon F. Detection of the CALR mutation in the diagnosis of splanchnic vein thrombosis. Br J Haematol 2015; 169:601-3.
Castro N Rapado I Ayala R Martinez-Lopez J. CALR mutations screening should not be studied in splanchnic vein thrombosis. Br J Haematol 2015; 170:588-9.
Plompen EP Valk PJ Chu I Darwish-Murad SD Plessier A Turon F et al. Somatic calreticulin mutations in patients with Budd-Chiari syndrome and portal vein thrombosis. Haematologica 2015; 100:e226-8.
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Ho WK Hong FS. CALR exon 9 mutations in idiopathic splanchnic vein thrombosis in an Australian cohort. Thromb Res 2017; 150:51-2.
Poisson J Plessier A Kiladjian JJ Turon F Cassinat B Andreoli A et al. Selective testing for calreticulin gene mutations in patients with splanchnic vein thrombosis: a prospective cohort study. J Hepatol 2017; 67:501-7.
Jain A Tibdewal P Shukla A. Calreticulin mutations and their importance in Budd-Chiari syndrome. J Hepatol 2017; 67:1111-2.
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Mo A Testro A French J Robertson M Angus P Grigg A. Early radiological intervention and haematology screening is associated with excellent outcomes in Budd-Chiari syndrome. Intern Med J 2017; 47:1361-7.
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Rai P Kumar P Mishra S Aggarwal R. Low frequency of V617F mutation in JAK2 gene in Indian patients with hepatic venous outflow obstruction and extrahepatic portal venous obstruction. Indian J Gastroenterol 2016; 35:366-71.
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