Pregnancy-associated desmoid fibromatosis: A Dutch multi-centre retrospective study

The development of desmoid fibromatosis (DF) is associated with pregnancy. The current treatment consensus recommends active surveillance (AS). However, data in pregnancy-associated DF is scarce and it is uncertain whether AS is the best management strategy for this DF-subgroup. The aim of this study was to describe demographic, tumor, obstetric, treatment characteristics and treatment outcome in pregnancy-associated DF.Female DF patients who were 18-50 years old at time of diagnosis (2000-2020) and had a history (≤5 years) of pregnancy at time of diagnosis were included.Overall, 62 patients were included. The most common locations were abdominal wall (74%), pelvis (10%) and extremities (10%). Mutational analysis was conducted in 31 patients of which 94% had CTNNB1-mutations. Ten patients (16%) were diagnosed during pregnancy, while the remainder were diagnosed after pregnancy with a median time from delivery to diagnosis of 19 months (1-60). The frontline management was AS in 38 patients (61%) of whom 12 (33%) developed progressive disease and surgery in 23 patients (37%). In total, 30 patients underwent surgery and five had local recurrence (17%). Positive resection margins were no prognostic factor. Nine patients received systemic treatment in second- or third-line.Pregnancy-associated DF generally has an indolent behavior, where our results underscore the difficulty of establishing a clear definition of this entity. This study shows that AS should be the frontline management strategy for pregnancy-associated DF. When active treatment is indicated, surgery is a good option with low recurrence rates, even with positive (R1) resection margins.