The experience with ruxolitinib is much more extensive than that with fedratinib: 5-year follow-up of the pivotal COMFORT trials reveals an overall survival (OS) advantage for patients randomized to ruxolitinib, despite crossover, and a median duration of spleen response of approximately 3 years; 15.8% of ruxolitinib-randomized patients in COMFORT-2 had improved bone marrow fibrosis after a median duration of treatment of 2.2 years and the allele burden of mutant JAK2 had declined by >20% in 31% of patients at week 192.6, 7, 8. This evidence concerns the gene JAK2 and primary myelofibrosis.