Retrospective world-wide registry on the efficacy of immune checkpoint inhibitors in alveolar soft part sarcoma : Updated results from sixty patients

11564 Background: Alveolar soft-part sarcoma (ASPS) is a highly metastasizing ultra-rare sarcoma subtype, frequently affecting young adults. Conventional cytotoxic drugs are not effective in ASPS, but antiangiogenics demonstrated significant improvement in tumor burden reduction and PFS in the only ever conducted comparative trial. Immune check-point (PD-1/PD-L1) inhibitors (ICI) are emerging promising drugs in the therapy of ASPS, from small reported retrospective and prospective series. A world-wide registry has been set up with the aim of exploring the efficacy of ICI in ASPS. Methods: Data from adult patients (pts) diagnosed with ASPS and treated with PD- 1/PD-L1 inhibitors for advanced disease in expert sarcoma centers from Europe, Australia and US was retrospectively collected. IRB approval was obtained. Demographics, data related to treatments and outcome were considered. Radiologic assessment was based on RECIST 1.1. Progression-free (PFS) and overall survival (OS) were calculated with Kaplan-Meier method. An updated analysis of this series is presented here. Results: Sixty ASPS pts (27 female/33 male) with a median age at diagnosis of 25y (range 3-61) were registered. Primary tumor arose in limbs in 47 pts (78%) and 41 pts (68%) were metastatic at diagnosis. 52/60 pts (87%) had received previous systemic therapy (including chemotherapy in 19 pts and antiangiogenics in 47pts), with a median of one previous line (0-6). All pts received ICI for metastatic disease. Immunotherapy regimens consisted of monotherapy in 31 pts (52%) and combination in 29 pts (48%) (23 with an antiangiogenic agent). 29/60 pts (48%) received ICI within a clinical trial. Among the 52 evaluable pts, there was 1 complete response (CR) and 20 partial responses (PR) (ORR 40.4%). After a median follow-up of 21 months -mos- (range 4-59), 37/60 pts have progressed to ICI, with a median PFS of 13.4 mos (95% CI 10.1-16.7). Eleven pts received a subsequent line of ICI with a median PFS of 26 mos (95%CI 0-57). 16 pts have died, being the median OS from ICI initiation 38 mos (95% CI 33-43). The 12-mos and 24-mos OS rates were 94% and 70% respectively. Conclusions: This registry constitutes the largest available series of ASPS treated with immune check-point inhibitors. Our results suggest that treatment with ICI provide long-lasting disease control and prolonged OS in pts with advanced ASPS, an ultra-rare entity with limited active therapeutic options. The results on subsequent ICI lines suggest a lack of cross-resistance among different ICI therapies.