1768P - Desmoid tumors: Experience of a Spanish reference center

Background

Desmoid tumors (DT) are rare, fibroblastic, locally aggressive neoplasms arising from deep tissues. Evidence regarding optimal treatment strategies remains scarce. We aimed to analyze the outcomes of different therapeutic approaches adopted at our center.

Methods

Retrospective analysis including patients (pts) diagnosed of DT and managed at our center between 2004-2024. Clinical and tumor characteristics were analyzed, as well as outcomes of different therapies.

Results

93 pts were included (median age 41, female sex 56%, n=52). Most frequent location was extra abdominal (44%, n=41), including trunk (19,3%, n=18), extremities (16%, n=15), and head and neck (8,6%, n=15); followed by intrabdominal (36,6% n=34) and abdominal wall (17,2% n=16). Median tumor size was 7 cm (range 1-30 cm). Molecular tissue-based analysis was conducted in 18 cases (20%) and a mutation in CTBBB1 was found in 9 pts (10%). Germline mutations in APC gene were identified in 16 pts (17%). Upfront active surveillance was adopted in 29 pts (31%), with a disease control rate of 48.3% (n=14; disease stabilization (DS) in 10 pts and tumor regression in 4 pts). Surgery was performed in 66 cases (70.2%) with a recurrence rate of 33% (n=22). Cryoablation was used in 7 pts (7,5%) with a response rate of 71,5% (n=5). 8 pts (8.6%) received radiotherapy. 39 pts (42%) received at least one systemic treatment (ST), including NSAIDs (10.3%, n=4), tamoxifen (7.7%, n=3), NSAIDs + tamoxifen (64.1%, n=25), chemotherapy (CT, 15.4%, n=6) and tirosin kinase inhibitors (1, 2.6%). CT was active in most patients (partial response (PR) in 66.6%, n=4); whereas tamoxifen +/- NSAIDs showed PR only in 15.6% (n=5). 18 pts received 2nd line ST, and 10 received ≥3 lines. After median follow-up of 43 months, 5 pts (5.4%) had died (1 tumor-related); 37 pts (39.8%) were alive with disease, 34 (36.5%) pts were alive with no disease, and 17 pts were lost (18.3%).

Conclusions

Our series confirms previous data regarding the role of active surveillance in the management of DT. Treatment with NSAIDs +/- hormone therapy did not show encouraging outcomes as indirectly compared to surveillance. Moreover, a high proportion of patients recurred after surgery, proving the need for other local treatments such as cryoablation, which showed promising activity in DT.

Clinical trial identification

Funding

Has not received any funding.

Disclosure

M. Arregui Valles: Financial Interests, Personal, Invited Speaker: Roche; Financial Interests, Personal, Other, Travel grants: PharmaMar; Financial Interests, Personal and Institutional, Coordinating PI: Lilly. All other authors have declared no conflicts of interest.