PURPOSE: The Myelofibrosis Symptom Assessment Form version 4.0 (MFSAF v4.0) comprises 7 common MF symptom items (fatigue, night sweats, pruritus, abdominal discomfort, pain under the left ribs, early satiety, bone pain) and is the first patient-reported outcome (PRO) instrument designed to assess MF symptom burden. Given that information on the psychometric properties of this instrument has been limited, we sought to evaluate its measurement properties and validate its use in the phase 3 MOMENTUM trial. METHODS: Data were pooled to assess MFSAF item distribution, structural validity, reliability (test-retest and internal consistency), construct validity (convergent, divergent, and known-groups), and sensitivity to change. Other PRO measures included Patient Global Impression of Severity/Change (PGIS/PGIC), EORTC QLQ-C30, PROMIS Physical Function Short Form 10b, and ECOG performance status. RESULTS: Participants (N = 195) showed high completion rates (>
93%) across 24 weeks. Moderate to strong Spearman correlation coefficients among items were mostly observed at baseline (range, 0.289-0.772) and week 24 (range, 0.391-0.829), which supported combining items into a multi-item scale and total score. Internal consistency (Cronbach's α, 0.877 at baseline and 0.903 at week 24) and test-retest reliability (intraclass correlation coefficient, >
0.829) were satisfactory across selected time intervals. Reliability was also supported by McDonald's omega (ω) coefficient (>
0.875). MFSAF moderately correlated with PRO measures of similar content, differentiated between PGIS and ECOG groups (P <
.001), and was able to detect change over time. CONCLUSIONS: The MFSAF v4.0 is a valid tool to assess MF symptom burden, supporting its use in future trials in similar populations.