Validation for use in Colombia of the EORTC QLQ–THY34 questionnaire to measure quality of life in patients with thyroid cancer

Abstract Purpose Although survival after thyroid cancer is favorable, many patients experience persistent symptoms and concerns that affect health-related quality of life (HRQoL). This study evaluated the measurement properties of the Colombian Spanish EORTC QLQ-THY34 in patients with thyroid cancer. Methods 500 adults treated at a national oncology referral center were included. Psychometric validation was conducted using Classical Test Theory (CTT) and Rasch analysis. CTT evaluated internal consistency; structural, convergent, and divergent validity; test–retest reliability, and responsiveness. Rasch analysis examined dimensionality, item and person fit, reliability, differential item functioning (DIF), and the relationship between item difficulty and patient responses using the person–item map. Results The empirical four-domain model: (Symptoms and Impact, Cancer-related Concerns, Oropharyngeal Alterations, and Lack of Social Support), fitted substantially better than the original 17-scale model, although RMSEA and SRMR remained above conventional thresholds. Internal consistency was adequate across domains, and Test-retest reliability was good for three domains and moderate in one. Responsiveness analyses showed statistically significant changes over time in the Symptoms and Impact and Cancer-Related Concerns domains. Rasch analysis indicated acceptable fit for most items, although some exhibited DIF, and suggested usefulness in patients with greater clinical complexity. Conclusion The Colombian Spanish EORTC QLQ-THY34 showed generally adequate measurement properties, supporting its use for assessing health-related quality of life in patients with thyroid cancer in Colombia. The empirically derived four-domain structure should be considered preliminary and requires replication in independent and more clinically diverse samples; meanwhile, the original EORTC scoring system should remain the standard for cross-study comparisons.