International single-arm phase II trial of pazopanib in advanced extraskeletal myxoid chondrosarcoma: A Collaborative Spanish (GEIS), Italian (ISG) and French (FSG) Sarcoma Groups study

11062 Background: Extraskeletal myxoid chondrosarcoma (EMC) is an exceedingly rare sarcoma, marked by a specific translocation involving the gene NR4A3 that can be rearranged with different partners. Preliminary retrospective data suggest that sunitinib is active, but no formal prospective studies are available. We report on a multicentric European prospective, investigator-driven, Phase 2 study on pazopanib (P) in NR4A3+ advanced EMC patients (pts), carried out by the Spanish, Italian and French Sarcoma groups. Methods: From June 2014 to November 2016, 24 advanced EMC pts entered this study (median age: 64 yrs - disease extent: metastatic 77%, locally advanced 23% - prior medical treatment: 18 (86%) naive; 2 (9%) 1 line, 1 (5%) > 1 line). Path diagnosis and NR4A3 rearrangement (FISH and/or real-time PCR analysis) were centrally confirmed. Pts received P 800 mg/day (relative dose intensity = 0,82%, 658 mg/day), until progression or toxicity. The primary study end-point was response rate as per RECIST 1.1. Secondary end-points were overall survival, progression-free survival (PFS), clinical benefit rate (CBR) (RECIST CR+PR+SD≥6mos). An exploratory evaluation of the correlation between the rearrangement subtype and the outcome is ongoing. Results: 20/24 pts were evaluable for response (1 early death; 3 too early). One patient (5%) had a partial response, 17 (75%) stable disease, 2 (10%) progression as their best RECIST responses. At the time of this analysis, 12 pts were still under treatment, while 12 interrupted P (10 progression, 1 toxicity, 1 other). At a 13-month median follow-up, the median PFS was 13 months (range 1.6-25.1), with 29% pts progression-free at 18 months and a 65% CBR. Median OS was not reached. Conclusions: This Phase 2 study is formally negative since the target of at least 3/21 RECIST responses was not reached. However, looking at PFS, P was associated with a prolonged disease stabilization in a significant proportion of pts. This suggests to further explore the use of P in EMC. Clinical trial information: NCT02066285.