Efficacy of liposomal doxorubicin in patients with intra- and extra-abdominal desmoid fibromatosis

11581 Background: Desmoid tumors (DT) or aggressive fibromatosis are rare growths of fibroblastic connective tissue that can be locally aggressive but without metastatic potential. Most cases are sporadic, but 5-20% of cases are associated with Familial adenomatous polyposis (FAP). Despite numerous systemic options, optimal choice is unclear, and there is a paucity of studies comparing efficacy based on tumor site. Liposomal doxorubicin (LD) can be an appealing option for DT patients (pts) given its favorable schedule and toxicity profile. In this study, we compared outcomes in pts with intra-abdominal (IA) and extra-abdominal (EA) DT who received LD. Methods: We identified pts with DT who were treated with LD between 1/2010 - and 2/2022 at two sarcoma centers. Tumor and pt characteristics and outcomes were clinically (symptom improvement) and radiologically (RECIST 1.1) assessed. Results: 40 pts with DT treated with LD were identified; 58% female and 42% male. Pt characteristics and outcomes are summarized in Table 1. Primary tumor site was IA in 21 (53%) pts. FAP was present more commonly in pts with IA vs EA DT, 8/21 (43%) and 4/19 (21%), respectively. In the IA cohort, LD was given as first (15/21, 71%), second (10%) or third (19%) line therapy. LD was used more commonly as a later line in the EA cohort with 16%, 52%, 16%, and 16% receiving it in first, second, third, and fourth lines, respectively. 37 pts were evaluable for response. Response rate in the IA cohort treated in first-line was 50% (8 of 16) and 10 of 12 evaluable pts had symptomatic improvement. No first-line responses were seen in the EA cohort. As later lines of therapy, 7/12 pts had disease control in the second line, 6/8 pts in the third line, and 1/2 pts in the fourth line with LD in the IA cohort. 1 patient had fourth line response to LD in the EA cohort. Disease control rate with LD was 72.5% across all pts. Reasons for early discontinuation of LD included progression or lack of symptom improvement (20%), allergic reaction (12.5%), adverse effects (7.5%), or infection (2.5%). No acute or long-term cardiotoxicity was reported. 2 pts had no signs of recurrence or symptoms at follow-up, 33 pts were alive with symptomatic DT, 1 patient died from disease, and 3 were lost to follow-up. Conclusions: In our study, LD provided tumor response, disease control, and symptomatic improvement regardless of location or prior therapy, with responses most frequently seen in IA DT in first line setting. Further studies should include comparison of efficacy, adverse effects, and patient-reported outcomes while accounting for tumor location and line of therapy. [Table: see text]