Which patients are candidates for JAK inhibitors and how to manage patients on JAK inhibitor treatment

Ruxolitinib indications and results Case 1 A 73-year-old woman with a longstanding history of essential thrombocythemia (ET), which has so far been well controlled with hydroxyurea, 1,000 mg orally daily, presents with a complaint of severe fatigue. She started feeling tired last year and thinks that her symptoms have gotten progressively worse over time. Her blood counts, usually performed every 6 months, have been within the normal range, but she has never experienced such profound fatigue before. She also noticed a 25-pound unintentional weight loss over the past 6 months. She used to be a very active woman and enjoyed hiking periodically with her husband, but now all she can do is light work at home and needs to take a nap at least twice during the day. A physical exam reveals a cachectic woman, with liver palpable 2–3 cm below the costal margin; her spleen is not palpable. Her most recent complete blood count (CBC) shows white blood cells (WBC) = 4.6 × 10⁹/L, hemoglobin = 93 g/L, and platelets =112 × 10⁹/L. A CBC performed 6 months earlier showed WBC = 4.2 × 10⁹/L, hemoglobin = 128 g/L and platelets = 168 × 10⁹/L. A peripheral blood (PB) smear reveals schistocytes and leukoerythroblastosis (2% blasts). A bone marrow (BM) biopsy is consistent with post-ET myelofibrosis (MF). Among the myeloproliferative neoplasms (MPN), MF is certainly the most challenging. It can manifest as a primary disorder or evolve from polycythemia vera (PV) or ET. MF imparts a significant burden on patients’ quality of life and can be associated with poor prognosis (median survival of 2–11 years depending on the risk category). The clinical hallmarks of MF include symptomatic splenomegaly and/or, less frequently, hepatomegaly, debilitating constitutional symptoms (e.g., extreme fatigue, weight loss, night sweats, pruritus, bone pain), and anemia. Historically, the results of MF treatment have been disappointing. Until recently, no drugs had been approved for this indication and management had relied purely on palliative measures, with no effect on the natural history of the disease. Various strategies have been utilized to treat massive splenomegaly (e.g., chemotherapy with hydroxyurea or cladribine, splenic radiation and splenectomy) or anemia (e.g., erythropoiesis-stimulating agents, danazol and immunomodulatory compounds, such as lenalidomide). Allogeneic stem cell transplantation is the only potentially curative approach, but it is associated with high rates of complication and mortality.