While the data continue to support the key role of ACVR1 inhibition together with JAK1 and JAK2 inhibition in the differentiated anemia benefit derived with momelotinib, they bring into question the use of BMF assessment at week 24 as a surrogate for clinical benefit and disease modification, given the lack of association between changes in BMF grade and OS and other efficacy outcomes. This evidence concerns the gene JAK2 and anemia.