Patients With Myelofibrosis Treated With Combination of Janus Kinase 2 Inhibitor and Erythropoiesis-stimulating Agent. A French Observational Study.

Myeloproliferative Neoplasms are chronic diseases; they encompass Polycythemia Vera, Essential Thrombocythemia, and Primary Myelofibrosis with shared mutations that constitutively activate the physiologic signal-transduction pathways responsible for hematopoiesis. Myelofibroses may arise either as primary or antecedent to Polycythemia Vera and Essential Thrombocythemia. Myelofibrosis is the least common and the most aggressive of these diseases leading to death in 5 to 7 years due to bone marrow failure, massive splenomegaly related to extra medullary hematopoiesis, constitutional symptoms and cachexia.

Until recently, treatment of Myelofibrosis consisted of supportive care only, especially transfusions.

Since 2005 driver mutations have been identified in more than 90% of patients with myeloproliferative neoplasms, providing substantial insight into their pathogenesis and leading to the development of JAK inhibitor drugs. Ruxolitinib, the first one available, has shown activity whatever the presence of Janus Kinase 2 mutation, in reducing splenomegaly, improving cytopenias, alleviating constitutional symptoms and finally improving survival (COMFORT I and II studies). In France, access to ruxolitinib has been possible since April 2011, before wider availability in November 2012.

Anemia is a frequent issue in Myelofibrosis, which may be managed by the use of Erythropoiesis-stimulating Agent, leading to a 40-50% response rate in small studies.

Consistent with its Janus Kinase 2 signalling inhibition, ruxolitinib therapy has been shown to be detrimental on the hemoglobin level, increasing the depth of anemia or transfusion need, especially during the first 12-24 weeks of treatment in the COMFORT studies.