(P 356) DESMOID TUMORS: A RETROSPECTIVE ANALYSIS FROM A REFERRAL CENTER

Objective: Desmoid tumors (DT) are rare, locally aggressive neoplasms with no metastatic potential but high risk of recurrence. Their unpredictable behavior makes management challenging. We present a retrospective series from a national sarcoma referral center, aiming to describe clinical features, treatment approaches and outcomes, and to identify prognostic factors.

Methods: We conducted a retrospective cohort study of patients with histologically confirmed DT treated at our center between 2011 and 2024. Event-free survival (EFS) was defined as the time from diagnosis to progression, treatment change, or death. Cumulative event rates were estimated using Kaplan-Meier method. Prognostic factors were analyzed using Cox proportional hazards models

Results: 109 patients were included (56.9% female; median age 36.8 years). Most frequent tumor sites were extremities/chest wall (n=44, 40.4%) and intra-abdominal (n=40, 36.7%9), followed by abdominal wall (n=17, 15.6%), and head and neck (n=8, 7.3%). First-line strategies included surgery (n=54, 49.5%), active surveillance (AS) (n=24, 22%), hormone therapy ± non-steroidal anti-inflammatory drugs (HT+/-NSAIDs) (n=20, 18.4%), systemic therapy (chemotherapy/tyrosine-kinase inhibitors) (n=6, 5.5%), cryoablation (CA) (n=4, 3.7%), and radiotherapy (n=1, 0.9%). Among patients undergoing upfront surgery, 35.8% experienced relapse (median relapse-free survival 26.5 months). In those managed with AS at some point (n=36), 22.2% showed spontaneous regression and 52.8% disease stabilization. CA (n=12) achieved a 69.5% response rate, and all responses were maintained after a median follow-up of 10.5 months. Median follow-up for the total cohort was 41.5 months. Median EFS was 57 months. In multivariate analysis, R1/R2 surgical margins (HR=2.26; p=0.006) and initial conservative approaches (AS or HT+/-NSAID) (HR=5.36; p=0.001) were independently associated with worse EFS. Tumor size >5 cm showed a non-significant trend (HR=2.00; p=0.10); and tumor location (p=0.55) and CTNNB1 mutation did not influence EFS (presence vs absence p=0.10, type of mutation p=0.96).

Conclusion: Our findings support individualized, multidisciplinary management of DT. AS (with or without HT+/-NSAIDs) are suitable for many, yet active therapy is often required. Surgery showed high relapse rates, and margins had a significant impact. Emerging therapies such as CA showed encouraging activity. Given the chronic nature of DT and potential treatment morbidity, shared decision-making is essential.