Lack of National Consensus for the Molecular Investigation of Myeloproliferative Neoplasms: Part 2

S. Langabeer
Cancer Molecular Diagnostics, St. James’s Hospital, Dublin 8


Dear Editor,

The diagnosis of a myeloproliferative neoplasm (MPN) requires consideration of clinical, haematological and bone marrow histo-morphological features. The description of the first MPN-specific molecular abnormality in 2005, the JAK2 V617F mutation, revolutionised the molecular diagnosis of these diseases. As this mutation is present in nearly all patients with polycythaemia vera and half of those with essential thrombocythaemia (ET) and primary myelofibrosis (PMF), assessment of this mutation was rapidly incorporated into classification systems. Subsequent genome sequencing studies of MPN identified recurrent mutations of the CALR gene in 2013. CALR mutations occur in up to 80% of JAK2 V617-negative ET and PMF cases and are almost mutually exclusive from the JAK2 V617F mutation. This information compels the inclusion of CALR mutation analysis into the MPN diagnostic algorithm after exclusion of the JAK2 V617F as evident in the most recent 2016 World Health Organization classification of myeloid malignancies.1 Given the previously documented centre-to-centre and clinician-to-clinician variation in ordering JAK2 V617F analysis,2 an audit was instigated to assess whether this deviation persisted in requesting the more recently described CALR mutations.

Prospective, diagnostic CALR requests on adults from a facility for haematological malignancy molecular diagnostics received in the four and a half years between January 2014 and June 2018 inclusive were included in the audit. CALR requests were analysed according to the requesting centre, all of which were hospital Haematology departments. Centres were excluded if the number of requests was ten or more in the audit period to eliminate those with smaller practices that would not routinely request CALR mutation analysis. The methodology for detecting mutations was unchanged throughout the audit period. A total of 1050 requests were received from 19 centres with the “hit-rate” calculated as the percentage of CALR positive cases divided by the overall number of requests. The median number of requests from all centres was 35 (range 10-188) with a median “hit-rate” of 14.4%. Conspicuously, a wide range in the individual centre “hit-rate” was evident, ranging from 4.8% (successful in less than 1 in 20 requests) to 28.6% (successful in more than 1 in 4 requests).

Evidently, indications for CALR mutation screening vary from haematology centre to centre implying a continued lack of national consensus approach to testing. That the “hit-rate” is less than that of 19.2% previously reported for the more common JAK2 V617F mutation is indeed confounding.2 Several reasons may be responsible with unfamiliarity with testing algorithms likely to be largely responsible. CALR mutation analysis is only indicated in those patients with suspected ET or PMF with strong evidence emerging that testing is not warranted in patients presenting with an erythrocytosis, even those with a low serum erythropoietin, nor in patients with a first or recurrent thrombosis.3,4 Findings are to be disseminated to all centres with further audits scheduled to reassess requesting patterns. This audit highlights certain impediments in implementing rapidly evolving, molecular diagnostic guidelines and emphasizes the need for continual education and adoption of a consensus approach for the molecular investigation of MPN, particularly in the context of defined laboratory resources.

Corresponding Author
Stephen E. Langabeer PhD FRCPath
Cancer Molecular Diagnostics
Central Pathology Laboratory
St. James’s Hospital
Dublin
D08 E9P6
Ireland
Tel: 01 4162353
Fax: 01 4103513
Email: slangabeer@stjames.ie


References

1. Arber DA, Orazi A, Hasserjian R, Thiele J, Borowitz MJ, Le Beau MM, Bloomfield CD, Cazzola M, Vardiman JW. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood 2016; 127: 2391-2405.
2. Langabeer SE. Lack of national consensus for the molecular investigation of myeloproliferative neoplasms. Irish Medical Journal 2015; 108: 189-190.
3. Catherwood MA, Graham A, Cuthbert RJG, Garrec C, Gardie B, Girodon F, Laird S, Cross NCP, McMullin MF. Absence of CALR mutations in idiopathic erythrocytosis patients with low serum erythropoietin levels. Acta Haematologica 2018; 139: 217-219.
4. Ianotto JC, Chauveau A, Mottier D, Ugo V, Berthou C, Lippert E, Delluc A. JAK2 V617F and calreticulin mutations in recurrent venous thromboembolism: results from the EDITH prospective cohort. Annals of Hematology 2017; 96: 383-386.

P845