Myelofibrosis (MF) is a rare hematologic malignancy that is characterized by dysregulation of the JAK-STAT pathway resulting in fibrosis of the bone marrow, splenomegaly, and abnormalities in peripheral blood counts including anemia, leukocytosis, and thrombocytopenia. This disease has 2 phenotypic extremes - myeloproliferative and cytopenic. Cytopenic myelofibrosis presents with pronounced cytopenia and a different landscape of genetic mutations which results in worse clinical outcomes and a poor prognosis. Patients with cytopenic MF are at high risk of developing various complications like bleeding, infections, and transfusion dependency. Historically, the only Federal Drug Administration (FDA) approved therapy was ruxolitinib, a JAK1/2 inhibitor, which improved constitutional symptoms and splenomegaly, however, exacerbated anemia and thrombocytopenia.1,2 There were very few options for patients with anemia and thrombocytopenia, and supportive treatments for these problems lack efficacy. Fortunately, there are newer treatment options which may allow for treatment of the symptoms and splenomegaly in the setting of cytopenias and even improve cytopenias. This up-to-date review not only highlights the prevalent options in therapeutic marketplace, but also sheds light on the significant unmet need of addressing anemia and thrombocytopenia in cytopenic MF.
Myelofibrosis (MF) is a chronic myeloid neoplasm characterized by myeloproliferation, bone marrow fibrosis, splenomegaly, and constitutional symptoms related to pro-inflammatory cytokine signaling. Biologically, MF is characterized by constitutive activation of JAK-STAT signaling; accordingly, JAK inhibitors have been rationally developed to treat MF. Following the initial approval of ruxolitinib in 2011, three additional agents have been approved: fedratinib, pacritinib, and momelotinib. As these therapies are noncurative, allogeneic stem cell transplantation remains a key treatment modality and patients with MF who are deemed candidates should be referred to a transplant center. This potentially curative but toxic approach is typically reserved for patients with higher-risk disease, and JAK inhibitors are recommended in the pretransplant setting. JAK inhibitors have proven effective at managing splenomegaly and constitutional symptoms and should be started early in the disease course in patients presenting with these clinical manifestations; asymptomatic patients may initially be followed with close surveillance. Drug-related myelosuppression has been a challenge with initial JAK inhibitors, particularly in patients presenting with a cytopenic phenotype. However, newer agents, namely pacritinib and momelotinib, have proven more effective in this setting and are approved for patients with significant thrombocytopenia and anemia, respectively. Resistance or disease progression is clinically challenging and may be defined by several possible events, such as increasing splenomegaly or progression to accelerated or blast phase disease. However, with multiple JAK inhibitors now approved, sequencing of these agents appears poised to improve outcomes. Additionally, novel JAK inhibitors and JAK inhibitor-based combinations are in clinical development.