Impact of JAK2(V617F) mutation status on treatment response to anagrelide in essential thrombocythemia: an observational, hypothesis-generating study

Abstract

Nicola Cascavilla,1 Valerio De Stefano,2 Fabrizio Pane,3 Alessandro Pancrazzi,4 Alessandra Iurlo,5 Marco Gobbi,6 Francesca Palandri,7 Giorgina Specchia,8 A Marina Liberati,9 Mariella D’Adda,10 Gianluca Gaidano,11 Rajmonda Fjerza,4 Heinrich Achenbach,12 Jonathan Smith,13 Paul Wilde,13 Alessandro M Vannucchi41Division of Hematology, Casa Sollievo della Sofferenza Hospital, IRCCS, San Giovanni Rotondo, Italy; 2Institute of Hematology, Catholic University, Rome, Italy; 3Department of Clinical Medicine and Surgery, University of Naples Federico II, Naples, Italy; 4Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy; 5Oncohematology Unit, Fondazione IRCCS Ca’ Granda, Ospedale Maggiore Policlinico, Milan, Italy; 6IRCCS AOU San Martino, Genova, Italy; 7Department of Specialistic, Diagnostic and Experimental Medicine, St Orsola-Malpighi Hospital, University of Bologna, Bologna, Italy; 8Unit of Hematology with Transplantation, Department of Emergency and Organ Transplantation, University of Bari, Bari, Italy; 9Ospedale Santa Maria, Terni, Italy; 10Division of Hematology, Azienda Ospedaliera Spedali Civili di Brescia, Brescia, Italy; 11Division of Hematology, Department of Translational Medicine, Amedeo Avogadro University of Eastern Piedmont, Novara, Italy; 12Research and Development, Shire GmbH, Eysins, Switzerland; 13Shire Pharmaceutical Development Ltd, Basingstoke, United KingdomAbstract: A JAK2(V617F) mutation is found in approximately 55% of patients with essential thrombocythemia (ET), and represents a key World Health Organization diagnostic criterion. This hypothesis-generating study (NCT01352585) explored the impact of JAK2(V617F) mutation status on treatment response to anagrelide in patients with ET who were intolerant/refractory to their current cytoreductive therapy. The primary objective was to compare the proportion of JAK2-positive versus JAK2-negative patients who achieved at least a partial platelet response (≤600×109/L) after anagrelide therapy. Of the 47 patients enrolled, 46 were included in the full analysis set (JAK2-positive, n=22; JAK2-negative, n=24). At 12 months, 35 patients (n=14 and n=21, respectively) had a suitable platelet sample; of these, 74.3% (n=26) achieved at least a partial response. The response rate was higher in JAK2-positive (85.7%, n=12) versus JAK2-negative patients (66.7%, n=14) (odds ratio [OR] 3.00; 95% confidence interval [CI] 0.44, 33.97). By using the last observation carried forward approach in the sensitivity analysis, which considered the imbalance in patients with suitable samples between groups, the overall response rate was 71.7% (n=33/46), with 77.3% (n=17/22) of JAK2-positive and 66.7% (n=16/24) of JAK2-negative patients achieving at least a partial response (OR 1.70; 95% CI 0.39, 8.02). There was no significant change in median allele burden over 12 months in the 12 patients who achieved a response. In conclusion, the overall platelet response rate was high in both JAK2-positive and JAK2-negative patients; however, a larger study would be required to confirm the differences observed according to JAK2(V617F) mutation status.Keywords: essential thrombocythemia, mutation, JAK2, anagrelide, treatment response, allele burden