Milea Timbergen

320 heterogeneous retrospective studies and other report contradictory results 53, 54 . To assess the true prognostic value of the S45F mutation for recurrence in a homogeneous group of patients, we performed a meta-analysis with individual patient data of patients with primary DTF treated with surgery only (reported in Chapter 7 ). We found that S45F mutated tumours do have a higher chance of recurrence compared to WT and T41A mutations. However, this risk of recurrence appeared to be mediated by tumour size and a higher chance of recurrence for S45F tumours was only valid for small tumours (<5 cm). This study suggests that a prognostic nomogram should not only focus on tumour site, size and age, but should also include CTNNB1 mutation status when predicting the risk of recurrence 38 . Health-related Quality of Life Whilst decreasing the risk of recurrence or achieving tumour stabilization or regression are the goal of many treatments, the effect of lowering symptoms must not be underestimated 55 . DTF remains a tumor with many faces; varying from a small, asymptomatic lump to a large infiltrative debilitating tumour and multiple recurrences. Especially in an unknown disease with a wide variety of clinical outcomes, evaluating HRQoL can be relevant to meet a patients’ need. To achieve this, more knowledge about the impact of the disease on a patients’ life is a necessity. Furthermore, a tool, designed specifically for DTF required. In Chapter 8 , 9 and 10 we describe the development of a DTF-specific questionnaire, the DTF-QOL, according to the guidelines of the European Organization for Research and Treatment for Cancer (EORTC) 56 . In Chapter 8 , we conducted a systematic literature review and organized patient focus groups to identify relevant HRQoL-issues. In Chapter 9 , the issues are ranked and prioritized by patients and health-care professionals. These two studies showed the impact of the disease on various domains of DTF patients and led to the initiation of the QUALIFIED study (The evaluation of health-related quality of life issues experienced by patients with desmoid-type fibromatosis), of which the protocol is described in Chapter 10 . This study includes the DTF-specific questionnaire, the ‘DTF-QOL’ which covers all HRQoL-domains. The results of this study will hopefully provide insight into the prevalence of HRQoL-issues and can be used to identify patients at risk for impaired HRQoL to improve our DTF care. 11