A two-tiered, single-arm, phase II trial of Vactosertib for anemic myeloproliferative neoplasm (MPN) patients was recently designed (NCT04103645) and will assess how well Vactosertib works in MPN patients to improve anemia and provide new information about how this agent blocks TGF-β signaling in MPN cells. Here, TGFB1 is linked to anemia.