(P 333) SYSTEMIC TREATMENT IN INTRA-ABDOMINAL DESMOID-TYPE FIBROMATOSIS: A SINGLE INSTITUTION RETROSPECTIVE CASE SERIES ANALYSIS

Objective: In the last years the management of desmoid-type fibromatosis (DTF) has changed, privileging a more conservative approach including active surveillance (AS) and limiting surgery. However, extra caution must be used in intra-abdominal DTF because of its critical anatomical site. Moreover, little is known about the role of systemic treatments in this specific subgroup. Herein, we report on the activity of systemic treatments in intra-abdominal DTF.

Methods: Data of patients (pts) with sporadic or FAP‐related intra‐abdominal DTF treated at our institution from 2007 to 2022 were retrospectively collected and analysed through descriptive statistics. A comparative analysis between FAP-related and sporadic DTF was conducted on patients, tumour characteristics and response to treatment. Tumour response was assessed retrospectively using RECIST criteria and building a waterfall plot of dimensional changes from baseline. PFS was estimated by the Kaplan-Meier method.

Results: 51 pts were included, 20 (39%) with FAP-related and 31 (61%) with sporadic DTF. Males were 27 (53%). The median age was 46 (range 20-77) yrs. Previous treatments were AS in 23 pts (45%), hormonal therapy in 12 (23.5%) and surgery in 16 (31.5%). Low-dose chemotherapy (ld-CT) was used in 49 pts (83%), 2 in second line, anthracyclines in 6 (10%), 4 in second line, and pazopanib in 4 (7%), 2 in second line. Reasons to start treatment included any radiological progression, symptoms and site at high risk of complications. In particular, symptoms were present in 61%, 100% and 50% of pts treated with ld-CT, anthracyclines and pazopanib, respectively. According to RECIST we observed: 1 CR (2%), 24 PR (50%), 21 SD (44%) of which 18 minor responses, including 2 after progression on anthracycline and pazopanib (fig. 1) and 2 PD (4%) with ld-CT; 2 PR (33%), both after progression on ld-CT, 3 SD (50%), including 2 after progression on ld-CT, with remarkable symptoms improvement and 1 (17%) PD with anthracycline; 1 PR (33%), 2 SD (67%), including 1 after progression on ld-CT with symptomatic benefit, with pazopanib. Symptoms improved in 80%, 66% and 50% of pts treated with ld-CT, anthracyclines and pazopanib, respectively. The median time to response was 11.5 (range 2-29), 6 (range 2-10), and 12 (range 3-14) mth with ld-CT, anthracyclines, and pazopanib, respectively. When considering FAP-related vs sporadic DTF, in the former we saw: 1) lower median age (41 vs 49 yrs; M 43 vs 59 yrs, F 41 vs 43 yrs); 2) more frequent multifocal presentation (50% vs 35%), 3) less AS (40% vs 48%) and 4) lower RECIST response to all therapies (37% vs 59%). Overall, 1 death due to concomitant lymphoma was seen. At a median follow-up (FU) of 33 mth, median PFS was 157 mth in the ld-CT group, with 8 PD; at a median FU of 25 mth (9-73 mth), in the anthracycline group, 1 PD was seen after 2 mth; and in the pazopanib group, with a median FU of 11.5 mth (range, 4-20 mth), we observed 1 PD after 17 mth.

Conclusion: Our analysis (the largest, to our knowledge) reflects our tendency in favour of a more conservative approach even in intra-abdominal DTF. The activity and efficacy of low-dose CT were confirmed, both in FAP-related and sporadic DTF. Anthracyclines may be successfully offered in case of progression and when a fast clinical response is required. New agents may obviously add to them.