(P 258) TO TREAT OR NOT TO TREAT: AN AUDIT OF INITIAL MANAGEMENT OF PATIENTS WITH DESMOID TUMOURS AT A SPECIALISED CENTRE

Objective: Desmoid tumours are benign but locally aggressive soft tissue tumours and may cause significant morbidity to patients related to pain and disfigurement. The natural history can be unpredictable with spontaneous regressions, indolent growth periods, and aggressive change with involvement of vital structures. Active surveillance is now the recommended initial management strategy for the majority of patients. If there is subsequent evidence of symptomatic progression or increasing morbidity, therapeutic recommendations should be tailored by considering the benefit and risk of each modality and include: surgery (margin clearance, functional outcome, disfiguring), radiotherapy (risk of second malignancy in young population) hormonal and systemic therapy (toxicities and treatment durations). The objective of this audit was to evaluate the initial management strategy for patients with desmoid tumours treated at our institution, particularly comparing initial active surveillance to upfront active treatment.Methods: We collected demographics, clinicopathological variables, initial management and follow-up status from patients with desmoid tumours identified from a sarcoma referral centre’s pathology archive between January 2012 and May 2022. Primary outcomes include recurrence-free survival (RFS, for initial surgery) and progression-free survival (PFS, for initial non-surgical intervention). Analysis is by Kaplan Meier and Cox regression methods.Results: We identified 79 patients with histologically confirmed desmoid tumours. Median age at diagnosis was 33 years (range 12-88). Baseline characteristics are summarised in Table 1. Median follow-up was 25 months (range 0-293). Initial management was active surveillance in 21 (27%) patients and therapeutic intervention in 58 (73%). Median recurrence/progression-free survival was 35.2m (95% CI 15-55; Table 2). Progression (or recurrence) was less common with initial management by radiotherapy (1/5, 20%) compared to surgery (14/46, 30%), active surveillance (9/21, 43%) or systemic therapy (6/7, 86%). PFS/RFS (median, HR, p-value) when compared to active surveillance (median 45m) was shortest for initial management by systemic therapy (12m, 4.2, 0.0017) followed by surgery (35m, 0.9, 0.81) and radiotherapy (NR, 0.4, 0.35); shown in Table 2 and Figure 1.Conclusion: This audit demonstrates the management pattern and outcomes of patients with desmoid tumours diagnosed at an Australian sarcoma centre confirming an initial active surveillance approach for those with disease not encroaching vital structures. For those with more rapidly progressing symptomatic disease therapeutic intervention with surgery, radiotherapy or systemic therapy can be considered; however initial active surveillance may still be appropriate. Biomarkers are urgently needed to help select patients for optimal management and predict for the failure of the active surveillance strategy. We plan further analysis of prognostic and predictive factors alongside correlative translational studies. Further study of different management strategies should also include patient-reported outcomes to guide treatment decision.MS and BZ are joint first authors.CTOS_Desmoid_Table1.pdfCTOS_Desmoid_Table2.pdfCTOS_Desmoid_Figure1.pdf