International phase IV field study to validate the European Organisation for Research and Treatment of Cancer questionnaire for assessing the health-related quality of life of cancer survivors: The EORTC QLQ-SURV100

Introduction Cancer survivors face unique and persistent health-related quality of life (HRQoL) challenges. Existing HRQoL questionnaires for survivors lack content regarding chronic physical issues and have typically included limited cancer types and languages/cultures, affecting breadth of content and generalisability. We developed and validated the EORTC QLQ-SURV100, a questionnaire to assess HRQoL in disease-free survivors of diverse cancers. A conceptual framework of HRQoL in cancer survivors, developed in previous study phases and conceptualised as survivors’ self-reported physical, mental and social functioning and well-being, formed the basis for questionnaire content. Methods The QLQ-SURV100 was administered to 1480 participants across 46 centres in 21 countries (31% breast cancer, 23% colorectal, 22% prostate, 24% other cancers), who had completed primary treatment 1–10 years earlier and had no evidence of active disease. Structural validity of the 21 multi-item questionnaire scales was assessed via confirmatory factor analysis; test-retest reliability via intraclass correlation coefficients (ICCs); construct validity through known-group comparisons; and cross-cultural validity and sex invariance through differential item functioning (DIF). Item response theory (IRT) analyses evaluated item redundancy and performance. Results The QLQ-SURV100 showed strong structural validity (Comparative Fit Index = 0.951; Tucker-Lewis Index = 0.944; Root Mean Square Error of Approximation = 0.046), with most standardised factor loadings ' 0.7. Test-retest ICCs exceeded 0.7 for 27 of 35 scales and 0.6 for 34 scales. Known-groups analyses supported most hypotheses, confirming sensitivity to treatment, comorbidity, age, sex, and education. DIF analysis indicated minor cross-cultural item bias, but no sex-related DIF. IRT analysis found no redundant items. Conclusions The EORTC QLQ-SURV100 showed satisfactory structural validity, test-retest reliability and construct validity; limited item redundancy; and measurement invariance across the sex and language groups examined.