Expert: Inhibits Janus kinase (JAK) 1 and JAK2 signaling pathways. In myelofibrosis, constitutive activation of JAK-STAT signaling (often via JAK2 V617F, CALR, or MPL mutations) drives myeloproliferation, splenomegaly, and constitutional symptoms. JAK inhibition normalizes cytokine signaling and reduces malignant clone proliferation.

Everyday: JAK enzymes are like switches that tell bone marrow cells to grow uncontrollably. In myelofibrosis, these switches are stuck "on" (often due to a JAK2 mutation). JAK inhibitors flip these switches off, shrinking the enlarged spleen and reducing symptoms like fatigue, night sweats, and bone pain.

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First-in-class JAK1/JAK2 inhibitor for myelofibrosis. Standard of care for MF with platelets >50K. CANNOT be used in severe thrombocytopenia (platelets <50K) - this is where Vonjo fills the gap. Also approved for polycythemia vera and acute/chronic GvHD. Facing generic entry ~2028 (US patent expiry).