Clinical evaluation of the European LeukaemiaNet criteria for clinicohaematological response and resistance/intolerance to hydroxycarbamide in essential thrombocythaemia

Br J Haematol. 2011 Jan;152(1):81-8. doi: 10.1111/j.1365-2141.2010.08430.x. Epub 2010 Nov 18.


Standardized criteria of response to treatment and a unified definition of resistance/intolerance to hydroxycarbamide (HC) in essential thrombocythaemia (ET) have been proposed by the European LeukaemiaNet (ELN). We have retrospectively evaluated such criteria in 166 ET patients treated with HC for a median of 4·5 years. Overall, 134 patients achieved a complete clinicohaematological response (CR) and 25 a partial response. Thirty-three patients met at least one of the ELN criteria defining resistance (n = 15) or intolerance (n = 21) to HC. Fifteen cases developed anaemia with thrombocytosis, which was associated with a high incidence of myelofibrosis and death from any cause. Other definitions of resistance were less useful. Factors determining the thrombotic risk were a history of prior thrombosis and a baseline leucocyte count >10 × 10⁹/ l. Of note, patients achieving a CR, even if sustained during the entire follow-up, did not benefit from a lower incidence of thrombosis or an improved survival. In conclusion, most ET patients respond to HC, but the achievement of response, as defined by the ELN, does not correlate with the patients' outcome. The best discriminating ELN criterion of resistance to HC was the detection of anaemia, which also identified a subgroup of patients with poor prognosis.

Publication types

  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Drug Evaluation / methods
  • Drug Evaluation / standards
  • Drug Resistance
  • Epidemiologic Methods
  • Female
  • Humans
  • Hydroxyurea / adverse effects
  • Hydroxyurea / therapeutic use*
  • Male
  • Middle Aged
  • Nucleic Acid Synthesis Inhibitors / adverse effects
  • Nucleic Acid Synthesis Inhibitors / therapeutic use*
  • Platelet Count
  • Prognosis
  • Thrombocythemia, Essential / blood
  • Thrombocythemia, Essential / complications
  • Thrombocythemia, Essential / drug therapy*
  • Thrombosis / etiology
  • Thrombosis / prevention & control
  • Treatment Outcome
  • Young Adult


  • Nucleic Acid Synthesis Inhibitors
  • Hydroxyurea