Milea Timbergen

200 IPD 15, 19, 23-25, 29-35 . Although there might be a selection, this is the largest cohort describing the correlation between CTNNB1 mutation type and recurrence risk to date. Despite these limitations, using the IPD of several international cohorts created a large pooled cohort of patient that received the same treatment, unique for a rare disease like DTF. The pooled data provided new insights into the prognostic value of the CTNNB1 mutation type in predicting local recurrence in surgically treated DTF patients, with tumour size as an important mediator. Currently, there are no prospective studies examining the value of adjuvant therapy after surgical resection of DTF. Future studies investigating the role of adjuvant therapy in patients with an S45F mutation, in whom re-resection would result in unacceptable morbidity, are recommended. Additionally, mechanistic studies, exploring how the different CTNNB1 mutations affect DTF tumour biology are warranted, especially since an increasing number of patients is being treated with active surveillance. Data from the three studies, that are currently investigating the active surveillance approach, will give valuable information regarding the association between CTNNB1 mutation type and DTF tumour behaviour. Conclusions Tumour size and mutation type should be considered as predictors for recurrence in patients with extra-abdominal, surgically treated primary sporadic DTF. Ongoing studies about upfront active surveillance, are evaluating whether mutation type can predict the risk of progression, to anticipate the need for treatment in patients who received an initial active surveillance approach. If the predictive value of mutation type for the risk of progression is proven, mutation type should be included in the algorithm for managing DTF. Acknowledgements We would like to thank Gerdien de Jonge, from the Medical Library, Erasmus MC - University Medical Center Rotterdam for her assistance with the literature search. 7