OBJECTIVES : To evaluate the psychometric performance of the National Comprehensive Cancer Network Functional Assessment of Cancer Therapy-Ovarian Symptom Index-18 (NFOSI-18) in a sample of patients with advanced ovarian cancer and to estimate clinically important differences (CIDs) in NFOSI-18 scores to guide interpretation.

METHODS : This cross-sectional study used real-world data from the Advanced Ovarian Cancer Disease Specific Programme™. Data was collected across Europe and the United States throughout 2017 from patients with ovarian cancer receiving chemotherapy. Patient-reported data were collected from the NFOSI-18, EQ-5D-5L, European Organisation for Research and Treatment of Cancer (EORTC) QLQ-C30, EORTC ovarian cancer module, and Work Productivity and Activity Impairment Questionnaire (WPAI). Data on treatment satisfaction, physician-reported symptoms, side effects, and disease status were also collected. Internal consistency reliability (Cronbach’s alpha) and construct validity (through Spearman’s correlations) were evaluated for the NFOSI-18 Total Score and its domains: Disease-Related Symptoms – Physical (DRS-P), DRS – Emotional (DRS-E), Treatment Side Effects (TSE), and Function and Well-Being (FWB). Anchor- and distribution-based methods generated clinically important between-group difference estimates, to enhance NFOSI-18 score interpretation guidelines.

RESULTS : Data from 897 patients aged 35-88 years were analyzed. Cronbach's alpha for all NFOSI-18 scores (total and domains) ranged from 0.81-0.83. The construct validity of scores was supported through correlations with convergent measures and ability to discriminate between known groups. Twelve patient-reported anchors (i.e., EORTC, WPAI, and satisfaction questionnaire items) were sufficiently correlated (r≥0.3 as recommended) with NFOSI-18 scores and were used to guide CID estimates. Across anchor- and distribution-based estimates, recommended CIDs are NFOSI-18 Total Score, 5-7; DRS-P, 3-4; DRS-E, 1; TSE, 2; FWB, 1-2.

CONCLUSIONS : Results provide evidence of score reliability and validity of the NFOSI-18. The generated CID estimates will help improve interpretation of between-group differences in NFOSI-18 scores in clinical trials for patients with advanced ovarian cancer.