Assessing new therapies and their overall impact in myelofibrosis.

Clinical management of myelofibrosis (MF)--whether primary or arising from an antecedent myeloproliferative neoplasm (post-essential thrombocythemia/polycythemia vera MF)--is currently in a period of transition that began with the discovery of the JAK2-V617F mutation 5 years ago. Selective JAK2 inhibitors have been developed, and clinical trials thus far have demonstrated that several of these agents meaningfully reduce MF-associated splenomegaly and constitutional symptoms. JAK2 inhibitors have durable benefits, act across the spectrum of MF subtypes, and provide a level of symptomatic benefit not seen with previous generations of nontargeted therapies. However, the JAK2 inhibitors can cause anemia and/or gastrointestinal disturbance, and their impact on JAK2 allele burden and the natural history is not yet fully defined. Several additional therapies that do not directly target JAK2 (eg, immunomodulatory drugs, histone deacetylase inhibitors, and inhibitors of the mammalian target of rapamycin [mTOR]) may ameliorate MF-associated anemia and morbidity-inducing symptoms. Balancing the potential benefits of these new agents against the risks and benefits of allogeneic stem cell transplantation (which can be curative, but carries a high risk of treatment-associated morbidity and mortality) requires an accurate estimation of the prognosis for an individual patient. Enhanced prognostic modeling systems are helping us to better characterize prognosis in MF patients not only at diagnosis, but also along the dynamic and variable course of the illness. Future advancements in the efficacy of MF-targeted therapy will likely arise from new pathogenetic insights and from combining JAK2 inhibitors with other agents.