Abstract
To assess the role of platelet (PLT) count for thrombotic complications in Essential Thrombocythemia (ET), 1201 patients followed in 11 Hematological centers in the Latium region were retrospectively evaluated. At multivariate analysis, the following factors at diagnosis were predictive for a worse Thrombosis-free Survival (TFS): the occurrence of previous thrombotic events (p = 0.0004), age greater than 60 years (p = 0.0044), spleen enlargement (p = 0.042) and a lower PLT count (p = 0.03). Receiver Operating Characteristic (ROC) analyses based on thrombotic events during follow-up identified a baseline platelet count of 944 × 109/l as the best predictive threshold: thrombotic events were 40/384 (10.4%) in patients with PLT count greater than 944 × 109/l and 109/817 (13.3%) in patients with PLT count less than 944 × 109/l, respectively (p = 0.04). Patients with PLT count less than 944 × 109/l were older (median age 60.4 years. vs 57.1 years., p = 0.016), had a lower median WBC count (8.8 × 109/l vs 10.6 × 109/l, p less than 0.0001), a higher median Hb level (14.1 g/dl vs 13.6 g/dl, p less than 0.0001) and a higher rate of JAK-2-V617F positivity (67.2% vs 41.6%, p less than 0.0001); no difference was observed as to thrombotic events before diagnosis, spleen enlargement and concomitant Cardiovascular Risk Factors. In conclusion, our results confirm the protective role for thrombosis of an high PLT count at diagnosis. The older age and the higher rate of JAK-2 V617F positivity in the group of patients with a baseline lower PLT count could in part be responsible of this counterintuitive finding.
The last sentence
helps explain the paradox.
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