Ayalew Tefferi & Animesh Pardanani
Momelotinib is an ATP-competitive small molecule inhibitor of Janus kinase proteins (JAKi), including JAK1, JAK2, JAK3, and TYK2; its other clinically relevant targets include activin A receptor type 1 (ACVR1), also known as activin receptor like kinase 2 (ALK2) [1]. Momelotinib was recently approved (September 15, 2023) for use in anemic patients with high/intermediate risk myelofibrosis (MF), including primary (PMF) [2] and secondary variants, the latter emerging from antecedent polycythemia vera (post-PV) [3] or essential thrombocythemia (post-ET) [4]. All three MF variants belong to the broader category of myeloproliferative neoplasms (MPNs), which are characterized by the presence of JAK-STAT activating mutations (JAK2, CALR or MPL) and predominantly megakaryocytic myeloproliferation with variable degrees of bone marrow fibrosis [5]. Patients with MF face premature death with 10-year survival estimates ranging from >80% in very low-risk diseases to <5% in very high-risk diseases [6]. In addition, the clinical course of the disease in MF is complicated by progressive anemia, extramedullary hematopoiesis with marked splenomegaly and hepatomegaly, constitutional symptoms, and cachexia. Causes of death in MF include disease transformation into acute myeloid leukemia [7].