D'Angelo, Sandra P

11008 Background: SARC028 is the first multicenter Phase II study of P monotherapy in patients (pts) with STS and BS. Designed to detect clinical efficacy signals in multiple histologies, the study collected blood & tissue samples on all pts. We report extended clinical follow-up and in-depth biomarker correlates of response. Methods: The primary endpoint was objective response rate (ORR) by RECIST 1.1. Secondary endpoints were safety, 12 wk progression-free survival (PFS), and overall survival (OS). The STS arm had 10 pts in each of 4 cohorts: undifferentiated pleomorphic sarcoma (UPS), dedifferentiated liposarcoma (DDLPS), synovial sarcoma (SS) and leiomyosarcoma (LMS). The BS arm included 40 pts with osteosarcoma (OS), Ewing sarcoma (ES) or dedifferentiated chondrosarcoma (CS). Pre- and on-P biopsies were required as well as blood at multiple time points. Tumor was assessed for PD-L1 expression (clone 22C3) and immune infiltrates by multi-color IHC (Vectra). Ongoing analyses include circulating cytokine and checkpoint levels and exome (DNA), transcriptome (RNA), and T-cell receptor (TCR) sequencing. Results: 86 pts were enrolled, 80 were evaluable for response. For STS, median follow-up was 14.5 months. The ORR in the overall STS cohort was 18% and the 12-wk PFS 55% [95% CI, 42-71]). Clinical activity was variable by histologic subtype with 40% ORR in UPS (1 CR and 3PR out of 10 evaluable pts), 2 PR/10 were seen in DDLPS, 1PR/10 in SS and 0/10 in LMS. For BS, median follow-up was 12.3 months (ORR 5%; 12-wk PFS 28% [95% CI, 14-41]), with 1PR/22 OS, 1PR/5 CS and 0/13 ES. 70 pre-P tissues were analyzed (11 excluded for insufficiency), with PD-L1+ in 3/70 (4%); all 3 were UPS. Of the 2 evaluable pts, 1 had CR and 1 PR. 2 OS were PD-L1+ on multi-color IHC, 1 had PR. All PD-L1+ samples had CD8+ T-cell infiltration. There were no post-P PD-L1+ samples. Conclusions: P has clinical activity in UPS and LPS, and expansion cohorts in those subtypes are planned. Pre-treatment PD-L1 expression was infrequent, but correlated with T-cell infiltration and response in UPS & OS. Ongoing biomarker analyses that may guide combination strategies are ongoing and will be presented at the meeting. Clinical trial information: NCT02301039.

11007 Background: Patients (pts) with metastatic sarcoma (SAR) have limited options. Nivolumab(N), a fully human anti-PD-1 mAb and ipilimumab (I), a humanized anti-CTLA-4 mAb, have favorable safety & efficacy in other tumors. Pembrolizumab demonstrated a response rate (RR) of 12% in SAR pts. We evaluated N, independently from N+I, in SAR pts. Methods: This open-label multi-center phase II study enrolled pts failing prior regimens. Randomized (non-comparative) pts received either N3 [N (3 mg/kg q2W)] or N3+I1 [N(3 mg/kg Q3W x4, then Q2W) & [I(1 mg/kg q3W x4)]. Treatment continued beyond progressive disease (PD) in 1st12 weeks. 5 confirmed responses in 38 evaluable pts yielded 90% power (0.05 1-sided alpha) to detect a 20% (vs 5%) confirmed RR. Other endpoints: adverse events (AEs), progression-free, overall survival (PFS, OS), and correlative studies including PD-L1 expression by IHC, mutational burden/neoantigen analysis, TCR clonality and TIL characterization. Results: 85 pts (43 - N3; 42 - N3+I1) were enrolled [mean age 54 yrs (21–81), 52% female). No significant differences in histological subtypes across cohorts: 36% LMS, 4% LPS, 10% UPS/MFH, 6% synovial, 5% bone, 5% Ewing’s, and 34% other. Pts were refractory to 1(20%), 2(22%), and ≥3 (58%) regimens. Grade 3-4 treatment related adverse events (TRAE) occurred in 7% (N3) and 14% (N3+I1) and 0 Gr 5 TRAEs. 8% of pts stopped due to AEs (2% N3, 14% N3+I1). 2/3 confirmed responses on N3, with 2 ongoing (range 1.1-3.2 months). 6/7 confirmed responses (2 complete) on N3+N1, with 5 ongoing (range 6-13 months). Responses occurred in 7 histologies. See Table for pt outcomes. Conclusions: N + I showed acceptable safety and encouraging antitumor activity with most responses ongoing across multiple SAR histologies, passing efficacy criteria. There was minimal activity observed with N alone. Increased TRAEs were observed in N3+I1. Correlative analyses ongoing. NCT02500797. Support: U10CA180821, U10CA180882, Conquer Cancer Foundation, BMS. Clinical trial information: NCT02500797. [Table: see text]