1650P Desmoid type fibromatosis in patients

Abstract

Desmoid type fibromatosis (DTF) are rare intermediate malignancies with unpredictable becoming. Guidelines recommend active surveillance (AS) first if few symptoms are present. The aim of this retrospective multicentric study is to describe the French population of patients <40 years with DTF registered in 2006-2017 in netSARC and CONTICABASE databases. Of 1526 patients registered, 964 patients were selected (median age (MA) 31 years, 83 children, F/M: 3.3). APC constitutional pathogenic variant was described in 4.6%. Primary tumor sites were abdominal wall (41%), trunk (23%), extremity (19%), mesentery (14%) and head and neck (HN) (3%); Median size was 55mm. MA was higher in patients with abdominal wall and mesentery sites (32 and 31.5 years) than in those with HN site (21 years, p=0.0001). Patients with familial adenomatous polyposis were 3 times more frequent in multifocal DTF group, and in mesenteric primary (p<0.001). Women of childbearing age were more frequent in the group “abdominal wall” than in the other groups (99.5% vs 96.8%, p=0.007) without increase of DTF diagnosis during pregnancy. First line strategy was known for 487 patients: AS (n=189, MA 31 years; treatment needed in a second time in 77 of them) versus front line treatment (n=298, MA 30 years), including most often surgery (280 patients, MA 31 years) or non surgical therapies (systemic treatment n=14, or cryotherapy n=4) (18 patients, MA 15 years, p<0.0001). With a median follow-up of 17 months [0; 142 months], the 1-year progression free survival (PFS) rate was 83.2% [80.2%-85.8%]. In univariate analysis, PFS was worse for young patients, male, tumor≥5cm, extremity and trunk sites, and APC constitutional pathogenic variant status. In multivariate analysis, size ≥5cm (HR=1.447, p=0.0923) and extremity primary (HR=1.6, p=0.0113) remained associated with worse PFS. Among the 487 informative patients, AS was associated with a better PFS (HR=0.694, p=0.0848). This series of patients identifies age, gender and constitutional related characteristics. AS seems to be a valid first line option. Such databases improve knowledge about risk factors for DTF and highlight the patients requiring care in expert centers.