Definition of subtypes of essential thrombocythaemia and relation to polycythaemia vera based on JAK2 V617F mutation status: a prospective study

doi:10.1016/S0140-6736(05)67785-9

The Lancet

Volume 366, Issue 9501, 3–9 December 2005, Pages 1945-1953

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https://doi.org/10.1016/S0140-6736(05)67785-9 Get rights and content

Summary

Background

An acquired V617F mutation in JAK2 occurs in most patients with polycythaemia vera, but is seen in only half those with essential thrombocythaemia and idiopathic myelofibrosis. We aimed to assess whether patients with the mutation are biologically distinct from those without, and why the same mutation is associated with different disease phenotypes.

Methods

Two sensitive PCR-based methods were used to assess the JAK2 mutation status of 806 patients with essential thrombocythaemia, including 776 from the Medical Research Council's Primary Thrombocythaemia trial (MRC PT-1) and two other prospective studies. Laboratory and clinical features, response to treatment, and clinical events were compared for V617F-positive and V617F-negative patients with essential thrombocythaemia.

Findings

Mutation-positive patients had multiple features resembling polycythaemia vera, with significantly increased haemoglobin (mean increase 9·6 g/L, 95% CI 7·6–11·6 g/L; p<0·0001), neutrophil counts (1·1×10⁹/L, 0·7–1·5×10⁹/L; p<0·0001), bone marrow erythropoiesis and granulopoiesis, more venous thromboses, and a higher rate of polycythaemic transformation than those without the mutation. Mutation-positive patients had lower serum erythropoietin (mean decrease 13·8 U/L; 95% CI, 10·8–16·9 U/L; p<0·0001) and ferritin (n=182; median 58 vs 91 μg/L; p=0·01) concentrations than did mutation-negative patients. Mutation-negative patients did, nonetheless, show many clinical and laboratory features that were characteristic of a myeloproliferative disorder. V617F-positive individuals were more sensitive to therapy with hydroxyurea, but not anagrelide, than those without the JAK2 mutation.

Interpretation

Our results suggest that JAK2 V617F-positive essential thrombocythaemia and polycythaemia vera form a biological continuum, with the degree of erythrocytosis determined by physiological or genetic modifiers.

Introduction

The human myeloproliferative disorders consist of three main diseases, essential thrombocythaemia, polycythaemia vera, and idiopathic myelofibrosis.¹ The main clinical features of essential thrombocythaemia are arterial and venous thrombosis, although haemorrhage can also occur.2, 3, 4 In a few patients the disease can proceed to myelofibrosis, acute myeloid leukaemia, myelodysplasia, or polycythaemia vera. The idea that essential thrombocythaemia might be heterogeneous is lent support by studies of X chromosome inactivation patterns,5, 6 PRV1 mRNA expression,7, 8 myeloproliferative leukaemia expression,9, 10 histological features,¹¹ and the presence of erythropoietin-independent erythroid colonies.⁸ However, where assessed, the concordance between these features is variable,⁸ and definition of biologically or pathogenetically distinct subgroups of essential thrombocythaemia has proved difficult.

Recently, a single somatic mutation of the Janus kinase 2 (JAK2) gene was reported in most patients with polycythaemia vera, but in only some patients with essential thrombocythaemia or idiopathic myelofibrosis.12, 13, 14, 15 The V617F mutation lies in the auto-inhibitory JH2 domain, and therefore increases JAK2 kinase activity, confers cytokine-independent growth on cell lines, and is associated with erythropoietin-independent growth of primary cells. Transplantation of bone marrow cells with mutant JAK2 results in erythrocytosis in vivo.¹³ By use of mutation-specific PCR, the JAK2 mutation was detected in peripheral blood granulocytes from around half of essential thrombocythaemia patients,¹² but whether mutation-bearing patients are biologically distinct from those lacking the mutation is not known, or why the same mutation is associated with different diseases. To address these questions, we have analysed samples from patients enrolled in three large prospective studies of high-risk, intermediate-risk, and low-risk essential thrombocythaemia.

Section snippets

Study population

Newly diagnosed and previously treated patients, aged 18 years or over, who met the Polycythemia Vera Study Group (PVSG) criteria¹⁶ for essential thrombocythaemia, were recruited into one of three multicentre studies: the Medical Research Council PT-1 trial,¹⁷ in which high-risk patients were randomly assigned to either hydroxyurea plus aspirin or to anagrelide plus aspirin; the National Cancer Research Institute intermediate risk study, a randomisation between aspirin alone or hydroxyurea plus

Procedures

Samples of peripheral blood were requested at trial entry from all patients, and 776 samples were received from the 1022 patients entered. Whole-blood genomic DNA was extracted commercially (Whatman International, Ely, UK). Allele-specific PCR and BsaXI digestion were done as described previously.¹² For platelet purification, blood was spun for 20 min up to three times, and the upper 50% of platelet-rich plasma used to extract RNA. Contaminating white cells were less than 1 per 10⁶ platelets.

Results

The V617F mutation was present in over half of patients (table 1), giving an overall frequency of 53%. We considered the possibility that essential thrombocythaemia patients without the V617F mutation in peripheral blood leucocytes might nonetheless carry the mutation in the megakaryocyte lineage. To investigate this possibility, we used allele-specific PCR to detect the mutation in purified platelet cDNA from ten patients. The results were completely concordant with those obtained with

Discussion

Our analysis of patients with essential thrombocythaemia enrolled in three prospective studies has shown that the JAK2 V617F mutation unequivocally divides the disease into two subtypes, with the V617F-positive group showing phenotypic similarities to polycythaemia vera. The combined cohort provides a unique resource for studying essential thrombocythaemia, especially in view of its large size, centralised review of endpoints, and comprehensive follow-up. Moreover, the participation of a large

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^‡: These authors contributed equally to this study

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ArticlesDefinition of subtypes of essential thrombocythaemia and relation to polycythaemia vera based on JAK2 V617F mutation status: a prospective study

Summary

Background

Methods

Findings

Interpretation

Introduction

Section snippets

Study population

Procedures

Results

Discussion

Blood

Blood Rev

Hematol Oncol Clin North Am

Blood

Blood

Blood

Blood

Lancet

Cancer Cell

Semin Hematol

Blood

Blood

Am J Med

Lancet

Articles
Definition of subtypes of essential thrombocythaemia and relation to polycythaemia vera based on JAK2 V617F mutation status: a prospective study