Milea Timbergen

190 disease, alive with evidence of disease, unknown), date of death, date of the last update of the database. Studies for which IPD was not provided were excluded from this analysis. Inclusion of patients using individual patient data Inclusion criteria for individual patients to be selected included: primary DTF tumour, age above eighteen years at diagnosis, treated with surgery alone, and known CTNNB1 mutation. Patients receiving neoadjuvant or adjuvant treatment, patients with rare CTNNB1 mutations, patients with intra-abdominal tumours or FAP, patients younger than 18 years, patients with missing data about recurrence, and patients with unknown CTNNB1 mutation type were excluded from the analysis (Supplemental Table 2). With respect to tumour sites, all papers applied different definitions for tumour sites. For data synthesis the following categories of tumour sites were applied: trunk/back (including the following terms: trunk, trunk superficial, abdominal wall, rectus abdominis, chest aperture, chest wall, flank, back, dorsal, prevertebral, scapular area, vertebra), head and neck (including the following terms: head/neck, neck, cervical) and extremity (including the following terms: extremity, upper extremity distal, upper extremity proximal, ulna, arm, elbow, shoulder, axilla, groin, inguinal, buttock, gluteal, calf, knee, lower leg, leg, popliteal, thigh, lower extremity proximal, lower extremity distal). One study failed to specify the extra-abdominal tumour site and these patients were categorized as having extra-abdominal DTF not specified (NS). In case the date of surgery was provided, age was calculated using date of birth and date of surgery. In case only the date of birth was provided, age was calculated using the date of birth and the date of diagnosis. In case age was provided in the cohort, it was defined in almost all cases as “age at surgery”. The median and mean age in years, the standard deviation (SD), and the interquartile range (IQR) were calculated for the total group and per cohort. Tumour size was obtained from the provided databases; however, specifics on how this variable was measured were lacking for every cohort. A single measurement of tumour size reported was assumed to be the largest diameter of the tumour. In case tumour size was given in multiple dimensions, the largest tumour size was used. All tumour sizes were converted into millimetres (mm). The mean tumour size (in mm), SD, median and IQR were calculated for the total group and per cohort. In case of non-normal distribution, log transformed values were used. Additionally, the percentiles (25th, 50th, and 75th) were used to create age and tumour size categories. 7