MPN fitness levels inform EFS, and change in MPN fitness risk is linked to EFS and clinical response. (A) EFS stratified by 4 MPN fitness levels (left) and quartiles of WB MAF (right). (B) Cox proportional hazards model associating PC1 to 3, shown in a 3-dimensional space, with risk of events to allow prediction of MPN fitness risk from serial samples. (C) EFS KM stratified by change in MPN fitness risk indicating statistically significant difference (left), and change in WB MAF, indicating no difference (right). (D) Cumulative incidence of partial or complete response stratified by change in MPN fitness risk indicating statistically significant difference (left), and change in WB MAF, indicating no difference (right). CI, confidence interval; HR, hazard ratio.