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

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.