The JAK2^V617F Mutation but NOT Platelet Parameters Predict Thrombotic RISK IN Patients with Philadelphia-Negative MYELOPROLIFERATIVE Disorders (MPDs).

Abstract 4984

Venous and arterial thromboses are important disease complications of both essential thrombocytopenia (ET) and polycythaemia vera (PV), the commonest MPDs. Predicting and managing this risk is not straightforward as the absolute platelet count does not necessarily correlate with thrombotic risk.

We retrospectively studied the platelet parameters, median platelet volume and platelet crit, in addition to the absolute platelet count using a Sysmex XE-2100 in patients with MPDs to determine if there was any relationship between these and subsequent thrombotic risk, as well as the JAK2^V617F gene status. This has not been done previously.

There were 82 patients (25 PV, 33 ET, 13 chronic idiopathic myelofibrosis, 11 MPD unclassifiable) with a median age of 63 (range 37-94). Thromboses occurred in 32/82 patients (26 venous, 6 arterial) after follow up of 12-108 months. The JAK2^V617F mutation was found in 77% of all patients. The median platelet count at diagnosis, prior to any therapy, of those patients who subsequently went on to experience a thrombotic event was not significantly different from those who did not: median platelet count 529 v 563 (p=0.06), median platelet volume 8.6 v 8.3 (p=0.36), platelet crit 0.49 v 0.5 (p=0.079).

Thrombosis was more likely to occur in those patients with a JAK2^V617F mutation; thrombosis occurred in 43 % of JAK2^V617F cases compared with 26% of cases without the mutation. The median platelet count in the JAK2^V617F unmutated group was higher than in the group with the mutation (620 v 530 p=0.04); other platelet parameters in the two groups did not show any difference based on the presence of the mutation (median platelet volume 8.2 v 8.6 (p= 0.29), median platelet crit 0.52 v 0.5 (p=0.06)).

We conclude that platelet parameters, as assessed by a modern automated haematology analyser, do not predict for thrombotic risk in patients with newly diagnoses MPDs. Other factors such as platelet dysfunction, inherited thrombophilia and underlying vascular disease risk factors may be important. Our findings support the notion proposed by others that the presence of the JAK2^V617F is a thrombotic risk factor.