JAK2 and neoplasm: Growing evidence indicates that oncogenic signaling alters the tumor microenvironment to support its own progression.1–3,46 We and others have previously shown that OSM is induced by JAK2 p.V617F or FLT3-ITD.5,7 We further investigated the effects of OSM on disease progression and fibrosis, its potential for genetic or pharmacologic inhibition, and its effects on T cells and myeloid cells in vivo.