GOunder/Desmoid Tumor Research Foundation DEsmoid Symptom/Impact Scale (GODDESS): psychometric properties and clinically meaningful thresholds as assessed in the Phase 3 DeFi randomized controlled clinical trial.

Purpose: The GODDESS tool was developed to assess Desmoid Tumor/Aggressive Fibromatosis (DT/AF) symptom severity and impact on patients' lives. This study evaluated GODDESS's cross-sectional and longitudinal measurement properties.

Methods: The Phase 3, randomized placebo-controlled, DeFi study (NCT03785964) of nirogacestat in DT/AF was used to assess GODDESS's reliability, construct validity, responsiveness, and estimate of meaningful change thresholds (MCTs). Other patient-reported outcome (PRO) measures included Patient Global Impression of Severity (PGIS) in DT/AF symptoms, EORTC QLQ-C30, Brief Pain Inventory Short Form, and PROMIS Physical Function short-form 10a v2.0 plus 3 items.

Results: DeFi participants (N = 142) had a median age of 34 years (range: 18-76) and were mostly female (64.8%), with extra-abdominal (76.8%) or intra-abdominal tumors (23.2%). The GODDESS symptom/impact scales showed internal consistency at baseline, cycles 4 and 7 (Cronbach's α > 0.70) and test-retest reliability (intra-class correlation coefficient > 0.85). GODDESS scales correlated moderately to highly with PRO measures capturing similar content and differentiated among PGIS and Eastern Cooperative Oncology Group groups. GODDESS scales detected improvement over time. For the total symptom score, a 1.30-point decrease was estimated as the within-person MCT and a 1.00-point decrease as the between-group MCT. For the physical functioning impact score, estimated within- and between-group MCTs were 0.60-point and 0.50-point decreases, respectively. Few participants exhibited symptom worsening.

Conclusion: GODDESS was found to be reliable, valid, responsive, and interpretable as a clinical trial endpoint in the pooled sample of DT/AF patients. Estimated MCTs can be used to define responders and assess group-level differences in future, unblinded, efficacy analyses.

Trial Registration Number And Registration Date: NCT03785964; December 24, 2018.