JAK2 and primary myelofibrosis: Moreover, Kroeger reported that this conditioning regimen induced a JAK-2 negativity in 78% of patients carrying the V617-JAK2 mutation before transplant24 and produced a rapid regression of bone marrow fibrosis in 59% of patients al day +100 and in 100% of patients at day +360.25 At present, the busulfan-fludarabine regimen could be considered as the RIC regimen that has been tested on the largest patient population and demonstrated the best results in terms of feasibility and clinical, molecular and histological responses.