Novel therapeutics for myelofibrosis.

Myelofibrosis (MF) includes primary MF, post-essential thrombocythemia MF, and post-polycythemia vera MF. MF is a progressive myeloid neoplasm characterized by ineffective clonal hematopoiesis, extramedullary hematopoiesis, a reactive bone marrow environment resulting in reticulin deposition and fibrosis, and a propensity for leukemia transformation. The identification of driver mutations in JAK2, CALR, and MPL has contributed to a better understanding of disease pathogenesis and has led to the development of MF-specific therapies, such as JAK2 inhibitors. Despite the fact that ruxolitinib and fedratinib have been clinically developed and approved, their use is limited due to adverse effects such as anemia and thrombocytopenia. Recently, pacritinib has been approved for a group of thrombocytopenic patients with significant unmet clinical needs. In symptomatic and anemic patients with prior JAK inhibitor exposure, momelotinib was superior to danazol in preventing exacerbation of anemia and in controlling MF-associated signs and symptoms, such as spleen size. Although the development of JAK inhibitors is remarkable, modifying the natural course of the disease remains a priority. Therefore, many novel treatments are currently under clinical development. Agents targeting bromodomain and extra-terminal protein, anti-apoptotic protein Bcl-xL, and phosphatidylinositol-3-kinase delta have been studied in combination with JAK inhibitors. These combinations have been employed in both the frontline and "add-on" approaches. In addition, several agents are being studied as monotherapies for ruxolitinib-resistant or -ineligible patients. We reviewed several new MF treatments in the advanced stages of clinical development and treatment options for cytopenic patients.