Desmoid type fibromatosis in pediatric and young adults from French databases: Clinical characteristics and initial outcome according to age

Background: Desmoid type fibromatosis (DTF) are rare intermediate malignancies with unpredictable outcome. Series containing children and young adults (YA) are lacking. Methods: The aim of this retrospective study was to describe the French population of patients<40 years with DTF diagnosed between 2006 and 2017. Results: Eighty-three children and 881 YA (18–39 years) were included (sex ratio M/F 1.3 and 0.25, respectively). Locations were abdominal wall (40.8%), trunk (23.5 %), extremities (19 %), mesentery (13.5 %) and head and neck (HN) (3.2 %). Tumors were larger in children (7 vs 5.5 cm for YA, p < 0.001), and more frequently located in the abdomen and mesentery in YA (p < 0.001). Patients with Familial Adenomatous Polyposis condition (5.3 % of the cases) were three times more frequent in the multifocal DTF group, and in mesenteric primary (p < 0.001). First-line strategy for 548 patients was: surgery (289 patients), active surveillance (AS, 189 patients), medical treatment (57 patients), other local treatment (radio/cryotherapy, 7 patients), or the combination of several active treatments (6 patients). The 2-year progression free survival (PFS) rate for the whole cohort was 68.3 %, better for YA (69.2 %) than for children (59.5 %, p = 0.0106). Among 548 informative patients, AS was associated with a better PFS (HR = 0.558) and the only variables associated with worse PFS in multivariate analysis were tumor size ≥ 5 cm (HR = 1.785) and location in the extremities (HR = 1.934) or trunk (HR=1.598). Conclusions: Clinical DTF presentation is more aggressive in children than YA. AS seems to be a valid first-line option preventing overtreatment, and local progression is linked to size and location, regardless of age.