Multi-institutional european single-arm phase II trial of pazopanib in advanced typical solitary fibrous tumors (SFT): A collaborative Spanish (GEIS), Italian (ISG), and French (FSG) sarcoma groups study

11038 Background: SFT is a ubiquitous uncommon soft tissue sarcoma with a pronounced hemangiopericytoma-like vascular pattern, exhibiting rich VEGF (tumor and endothelial cells) and VEGFR1/2 (endothelial cells) expression. Pathologists distinguish typical SFT (T-SFT) and malignant SFT (M-SFT) based on mitosis (≤4 vs > 4), pleomorphism or necrosis. Yet, not clear boundaries are always seen between both subtypes. We have recently published a phase II trial exploring the activity of pazopanib (P) in M-SFT (Lancet Oncol Dec 2018). Here, we present the outcome of the T-SFT cohort of the same trial. Methods: Most relevant inclusion criteria were: unresectable or metastatic, T-SFT (tumor tissue from diagnostic time) confirmed by central pathology review before accrual, with evidence of STAT6 overexpression (IHC and FISH and/or NGS), ≥18 years, ECOG 0-2, progressive, measurable disease and no previous antiangiogenic agents. Main endpoint was response rate according to Choi criteria. Central radiological assessment was mandatory. P was administered at 800 mg/d continuously till progression or toxicity. Results: From June 2014 to December 2018, 34 patients were enrolled in this cohort. The median age was 64 y (31-81). At baseline, ECOG 0/1/2 was distributed as 16/15/3; whereas, locally advanced/metastatic distribution was 11 (32%) and 23 (68%) respectively. At the time of the present analysis, 24 patients were deemed eligible and evaluable for response. Response rates according to local and central assessment were PR 6 (25%), SD 15 (62%), PD 3 (12%) and PR 12 (50%), SD 11 (46%), PD 1 (4%). With a median follow-up of 21 months, the median PFS following local and central assessment were 18.4 (6.6-30.1) and 9.8 (7.5-12.2) months respectively, both were clearly superior to that previously published in M-SFT cohort (5.57 m). The median of OS was 49.8 months. High tumor burden at baseline > 116 mm, ECOG 1-2 vs 0, and PD by local or central response assessment showed significantly worse OS. Metastatic vs locally advanced patients had a similar outcome regarding OS. Conclusions: T-SFT cohort exhibited clearly longer PFS than previous reported M-SFT cohort to pazopanib treatment, and pazopanib showed to improve the historical outcome obtained with chemotherapy in advanced SFT. Clinical trial information: NCT02066285.