Measuring What Matters for Breast Cancer Survivors: Translation, Cross-Cultural Adaptation and Validation of the Croatian Version of Lymphedema Quality of Life Tool-Arm.

Background: Breast cancer-related lymphedema is a common long-term complication of breast cancer treatment that affects physical functioning, emotional well-being, and quality of life. Although the Lymphedema Quality of Life Questionnaire-Arm (LYMQoL-Arm) is widely used internationally, no Croatian version has been available. The primary objective of this study was to translate and validate the Lymphedema Quality of Life Questionnaire-Upper Limb-Croatian (LYMQoL-UL-CRO) version and evaluate its psychometric properties. A secondary objective was to examine associations between its scores and the relative volume change (RVC) of the affected limb to assess construct validity further. Methods: A retrospective cross-sectional study was conducted in 87 women at least six months post-treatment. The questionnaire was translated using a forward-backward procedure. Participants completed the LYMQoL-UL-CRO, the Short Form-36 Health Survey (SF-36), Pain Intensity Numerical Rating Scale, and underwent clinical examination and limb-volume assessment. Test-retest reliability was assessed in 68 participants after 10 days. Psychometric analyses included internal consistency, intraclass correlation coefficients, measurement error indices, construct and discriminant validity tests, exploratory factor analysis, and evaluation of floor and ceiling effects. Results: LYMQoL-UL-CRO domains demonstrated acceptable to strong internal consistency and moderate test-retest reliability, with low measurement error. Strong negative correlations with the SF-36 Physical Component Summary supported construct validity, and participants with RVC ≥ 5% reported worse scores, supporting discriminant validity. Exploratory factor analysis confirmed the original four-factor structure, and no floor or ceiling effects were observed. Conclusions: The LYMQoL-UL-CRO is a reliable, valid, and culturally appropriate tool for assessing quality of life in Croatian breast cancer survivors with upper-limb lymphedema.