Myelofibrosis with myeloid metaplasia following essential thrombocythaemia: actuarial probability, presenting characteristics and evolution in a series of 195 patients.

Myelofibrotic transformation is a known complication of essential thrombocythaemia (ET), but information on its incidence, presenting features and evolution is scarce. In a series of 195 patients with ET followed for a median of 7.2 years (range: 1.9-24), evolution into myelofibrosis with myeloid metaplasia (MMM) occurred in 13 cases, a median of 8 years (range: 3.6-20.2) from diagnosis. The actuarial probability of this complication was 2.7% (95% CI: 2.4-2.9) at 5 years, 8.3% (95% CI: 7.8-8.9) at 10 years, and 15.3% (95% CI: 6.1-24.5) at 15 years. Four patients had not been treated before developing MMM. The main features indicating this condition were the appearance of immature myeloid precursors in the peripheral blood, a decrease in the Hb value not related to treatment and increased serum lactate dehydrogenase levels, followed by a progressive decrease in the platelet count, increasing leucocytosis and progressive splenomegaly. No patient had constitutional symptoms, and none of five evaluable cases showed chromosome abnormalities in bone marrow or unstimulated blood. After a median the myelofibrotic transformation, three patients have died and four have not required treatment for MMM as yet.