Milea Timbergen

260 the questionnaire. When this tool has been developed and validated, it will reflect overall patient experience and its multidimensional contributing factors by including important non- symptom, disease specific areas regarding the unpredictable course of this rare disease. The tool could be used alongside the EORTC QLQ-C30, to gain more insight into HRQoL-issues of the patient at diagnosis. Additionally, longitudinal studies could evaluate HRQoL-issues of DTF patients during their disease trajectory and the questionnaire can potentially be used in both clinical and research setting. Conclusions This study identified relevant issues for DTF patients to be considered in the future development of a DTF-specific HRQoL-questionnaire. Issues regarding the unpredictable growth behaviour and rarity of DTF were the most highly ranked by patients and HCPs. Additionally, this study identified differences in priority scores between British and Dutch patients. Although this could be due to selection-bias, field-testing in a large, international cohort is needed to confirm any potential cultural findings. Acknowledgments The authors would like to thank the patients and health care providers who took part in this study. Funding Statement We would like to acknowledge the funding and support from Stichting Coolsingel, Rotterdam, the Netherlands (grant number 566), the NIHR Biomedical Research Centre at The Royal Marsden and the Institute of Cancer Research, London (NIHR RM/ICR BRC) and the National Institute for Health Research Clinical Research Network (NIHR CRN). Dr. Olga Husson is supported by a Social Psychology Fellowship from the Dutch Cancer Society (#KUN2015-7527). 9