MRI may be used as a prognostic indicator in patients with extra-abdominal desmoid tumours

Objective: To determine the association of MRI features of extra-abdominal desmoid tumours (DTs) with prognosis. Methods: MRIs for 90 patients with DT were retrospectively reviewed for imaging features associated with biological behaviour. The primary end point was progression (for lesions managed with chemotherapy, radiation therapy and observation) or recurrence (following surgery). Time to event was studied using univariate and multivariable Cox proportional hazards regression models when accounting for demographic, clinicopathological and imaging variables. Kaplan-Meier plots were used to estimate event-free rate (EFR). Results: Univariate analysis revealed a significant relationship between EFR and treatment, location and compartment of origin [subcutaneous (SC), superficial fascial, intramuscular (IM) and deep fascial/intermuscular]. None of the imaging features commonly associated with biological behaviour of DTs (e.g., shape, enhancement, T2 signal etc.) or surgical margins (in surgical cases) was associated with EFR. Multivariate analysis showed that treatment modality and compartment of origin were independent predictors of EFR. Superficial and deep fascial lesions had a significantly worse EFR as a group [hazard ratio: 3.9; 95% confidence interval (CI): 1.83-8.32; p50.0004] than did the SC and IM lesions as a group. 5-year EFR for the fascial lesions was 18% (95% CI: 6-36%), compared with 57% (95% CI: 25-79%) for the SC and IM groups. Conclusion: Intramuscular or SC DTs may be associated with improved prognosis. If validated on multireader and prospective studies, these results can provide for rapid risk stratification at the time of initial MRI. Advances in knowledge: This work has shown that imaging features commonly associated with biological activity of desmoid tumours (e.g. shape, T2 signal and enhancement) do not appear to be associated with prognosis in patients undergoing a variety of treatment modalities. The compartment of origin of the lesion, which can be determined on pre-operative MRI, was shown to be associated with prognosis and can allow for risk stratification in patients with DTs.