BackgroundTo better quantify the impact that breast cancer-related arm lymphedema (BCRL) has on health-related quality of life (HR-QOL), a disease-specific patient-reported outcome measure (PROM) is needed. The LYMPH-Q Upper Extremity Module was recently developed for patients with BCRL. The aim of this study was to perform an advanced translation and culturally adapt the LYMPH-Q Upper Extremity Module for use in Denmark.MethodsThe LYMPH-Q Upper Extremity Module was translated into Danish according to the guidelines of the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) and the World Health Organization (WHO). The process included two forward and one back translation, an expert panel meeting, and cognitive debriefing interviews with patients. The focus of the translation was to develop a Danish version that used appropriate patient-friendly language while maintaining the meaning of the items, instructions and response options.ResultsThe two forward translations resulted in minor differences in terminology. These discrepancies were discussed among the translators and a harmonized Danish version 1 was achieved. Comparison of the back translation to the original English version identified 14 items/instructions/response options that required re-translation. Subsequently, experts helped to identify and resolve the language for 10 items/instructions/response options that did not maintain the same meaning as the English version. Participants in the cognitive debriefing interviews did not report any difficulties with understanding the items/instructions/response options.ConclusionsThe translation and cultural adaption process led to the development of a conceptually equivalent Danish version of the LYMPH-Q Upper Extremity Module.Level of Evidence: Not gradable