Treatment options for patients with advanced biliary tract cancer are limited. Dysregulation of the immune system plays an important role in the pathogenesis of biliary tract cancer (BTC). This study aimed to investigate whether tremelimumab, an anti-CTLA4 (cytotoxic T-lymphocyte-associated protein 4) inhibitor, could be combined safely with microwave ablation to enhance the effect of anti-CTLA4 treatment in patients with advanced BTC. Patients were enrolled to receive monthly tremelimumab (10 mg/kg, intravenously) for six doses, followed by infusions every 3 months until off-treatment criteria were met. Thirty-six days after the first tremelimumab dose, patients underwent subtotal microwave ablation. Interval imaging studies were performed every 8 weeks. Adverse events (AEs) were noted and managed. Tumor and peripheral blood samples were collected to perform immune monitoring and whole-exome sequencing (WES). Twenty patients with refractory BTC were enrolled (median age, 56.5 years). No dose-limiting toxicities were encountered. The common treatment-related AEs included lymphopenia, diarrhea, and elevated transaminases. Among 16 patients evaluable for efficacy analysis, 2 (12.5%) patients achieved a confirmed partial response (lasting for 8.0 and 18.1 months, respectively) and 5 patients (31.3%) achieved stable disease. Median progression free survival (PFS) and overall survival (OS) were 3.4 months (95% confidence interval [CI], 2.5-5.2) and 6.0 months (95% CI, 3.8-8.8), respectively. Peripheral blood immune cell subset profiling showed increased circulating activated human leukocyte antigen, DR isotype ([HLA-DR] positive) CD8 + T cells. T-cell receptor (TCR)β screening showed tremelimumab expanded TCR repertoire, but not reaching statistical significance (P = 0.057). Conclusion: Tremelimumab in combination with tumor ablation is a potential treatment strategy for patients with advanced BTC. Increased circulating activated CD8 + T cells and TCR repertoire expansion induced by tremelimumab may contribute to treatment benefit. (Hepatology 2019;69:2048-2060).

The effectiveness of immune checkpoint inhibitors (ICI) is limited in pancreatic ductal adenocarcinoma (PDAC). We conducted a phase I study to evaluate the safety of ICI with stereotactic body radiation therapy (SBRT) in patients with metastatic PDAC.Patients and Methods: Patients enrolled must have received at least one line of prior systemic chemotherapy for metastatic disease. Cohorts A1 and A2 received durvalumab every 2 weeks plus either 8 Gy in one fraction of SBRT on day 1 or 25 Gy in five fractions on day À3 to þ1. Cohorts B1 and B2 received durvalumab plus tremelimumab every 4 weeks and either 8 Gy in one fraction of SBRT on day 1 or 25 Gy in five fractions on day À3 to þ1. ICIs were continued until unacceptable toxicity or disease progression. The primary objective was the safety and feasibility of treatment. Objective response was assessed in lesions not subjected to SBRT.Results: Fifty-nine patients were enrolled and 39 were evaluable for efficacy. No dose-limiting toxicities were seen. The most common adverse event was lymphopenia. Two patients achieved a partial response (one confirmed and the other unconfirmed). The overall response rate was 5.1%. Median PFS and OS was 1.7 months [95% confidence intervals (CI), 0.8-2.0 months] and 3.3 months (95% CI, 1.2-6.6 months) in cohort A1; 2.5 months (95% CI, 0.1-3.7 months) and 9.0 months (95% CI, 0.5-18.4 months) in A2; 0.9 months (95% CI, 0.7-2.1 months) and 2.1 months (95% CI, 1.1-4.3 months) in B1; and 2.3 months (95% CI, 1.9-3.4 months) and 4.2 months (95% CI, 2.9-9.3 months) in B2.Conclusions: The combination of ICI and SBRT has an acceptable safety profile and demonstrates a modest treatment benefit in patients with metastatic PDAC.

336 Background: Prognosis in advanced HCC and BTC is unfavorable, and 5-year overall survival (OS) rate is less than 20% and 10%, respectively. Single agent ICI in HCC has response rates (RR) of 20%, while early data in BTC reported 17.4% RR. Dual ICI has increased RR in other malignancies. The purpose of this study was to explore the efficacy of the combination of anti-CTLA4 (tremelimumab) with anti-PD-L1 (durvalumab) in advanced HCC and BTC. Methods: Eligible patients with advanced HCC or BTC who had received (or refused) at least one prior therapy, received monthly tremelimumab 75 mg in combination with durvalumab 1500 mg for 4 doses followed by monthly durvalumab 1500 mg monotherapy until progression of disease or unacceptable toxicity. Response was assessed with CT scan every 8 weeks. Adverse events (AEs) were recorded and managed. The primary endpoint is 6-month progression free survival (PFS). Results: Twenty-two patients were enrolled, 10 with advanced HCC and 12 with advanced BTC. Male to female ratio was 14:8, with median age of 62.5 years (range 19-80). Grade 3/4 treatment-related AEs included lymphocytopenia, hyponatremia, bullous dermatitis, maculopapular rash, mucositis, hypophosphatemia, anaphylaxis, dyspnea, pleural effusion, and pain. Twenty patients were evaluable for response analysis. Two patients (2/10, 20%) achieved a confirmed partial response (both with HCC, lasting 6.9 and 17.6 months), while 9 patients (4 [40%] with HCC and 5 [41.7%] with BTC) had stable disease, with the longest duration of 9.3 months (in an HCC patient). Disease control rate is 60% in HCC and 41.7% in BTC, respectively. In this small pilot cohort, median PFS was 3.1 months (95% CI 0.8 to 4.6 months) and median OS was 5.45 months (95% CI 4.60 to 8.3 months) among BTC patients, while HCC patients median PFS was 7.8 months (95% CI 2.6 to 10.6 months) and median OS was 15.9 (95% CI 7.1 to 16.3 months). Conclusions: Combined ICI with tremelimumab and durvalumab is well tolerated and demonstrates promising activity in patients with advanced HCC and BTC. Clinical trial information: NCT02821754.

This study aimed to investigate the benefit of combining immunotherapy (AMP-224) with radiation for patients with metastatic colorectal cancer. Fifteen patients were enrolled. No objective response was observed although 3 patients (20%) had stable disease. A signal of immune modulation was noted. Background: The prognosis of metastatic colorectal cancer (mCRC) is poor. We assessed the feasibility, safety, and efficacy of the anti-programmed cell death 1 fusion protein AMP-224 in combination with low-dose cyclophosphamide and stereotactic body radiation (SBRT) treatment in patients with mCRC refractory to standard chemotherapy. Patients and Methods: Fifteen patients were enrolled. Six received SBRT 8 Gy on day 0 (dose level 1), whereas 9 received 8 Gy on days À2 to day 0. All received cyclophosphamide 200 mg/m 2 intravenously (I.V.) on day 0. On day 1, both groups received AMP-224 10 mg/kg I.V., repeated every 2 weeks for a total of 6 doses. Primary end points were feasibility and safety. Results: Ten (67%) patients completed 6 doses of AMP-224; 5 patients (33%) discontinued treatment because of disease progression. No dose-limiting toxicity was observed; 9 patients (60%) experienced treatment-related adverse events, all Grade 1 or 2. No objective response was noted; 3 patients (20%) had stable disease. Median progression-free survival and overall survival were 2.8 months (95% confidence interval [CI], 1.2-2.8 months) and 6.0 months (95% CI, 2.8-9.6 months), respectively. M2 macrophage polarization was present in the pretreatment tumor biopsy samples, but not post-treatment samples. Conclusion: AMP-224 in combination with SBRT and low-dose cyclophosphamide was well tolerated, however, no significant clinical benefit was observed in patients with mCRC.

117 Background: The benefit of immune checkpoint inhibition is limited to the small percentage of advanced colorectal cancer (CRC) patients whose tumors present mismatch repair (MMR) gene abnormalities; immunotherapy has not shown benefit in patients with MMR proficient CRC. Oncolytic immunotherapy represents a unique therapeutic platform. This phase I trial tests the safety of the combination of pexastimogene devacirepvec (Pexa-Vec) plus durvalumab (durva) in patients with locally advanced or metastatic CRC. Methods: Eligible patients with advanced proficient mixed match repair (pMMR) CRC received intravenous infusion of Pexa-Vec at dose level 3 x 108 plaque forming units (pfu) (DL1) or at 109 pfu (DL2) every 2 weeks for 4 doses and durva 1500 mg every 28 days. Response was assessed with CT every 8 weeks. Adverse events were recorded and managed. The primary endpoint included safety, tolerability and feasibility of this combination therapy. Samples of tumor and peripheral blood were collected for assessment of immune parameters. Results: Sixteen patients (6 males and 10 females) enrolled with a median age of 52.1 years (range 39-69) from Dec, 2017 to Oct, 2018. Four patients were treated with Pexa-Vec at DL1 and durva;twelve patients were treated with Pexa-Vec at DL2 and durva.The most common treatment related adverse events (TRAE) included fever 15/16 (94 %), hypotension 12/16 (75 %), chills 12/16 (75%), fatigue 8/16 (50%), sinus tachycardia 7/16 (44%) and rash 6/16 (38%). Grade 3/4 TRAEs were reported in 8/16 (50%)patients; the most common were fever 7/16 (44 %), lymphopenia 2/16 (13%), neutropenia 1/16 (6%) and anemia 1/16 (6%). 14 patients were evaluable for response analysis; one patient 1/14 (7 %) achieved a confirmed partial response (lasting 7.1 months) and continues to receive treatment, while 13 patients had progressive disease. The median progression free survival (PFS) was 2.2 months (95% CI: 2.2-2.3 months) and the median overall survival (OS) was 7.5 months (CI: 4.9-10.1 months). Conclusions: Combination therapy of Pexa-Vec with durva ICI issafe, well tolerated and demonstrates possible activity in patients with advanced pMMR CRC. Clinical trial information: NCT03206073.

646 Background: The efficacy of immune checkpoint inhibitor has been limited to small portion of colorectal cancer (CRC) patients whose tumors with mismatch repair (MMR) gene abnormalities. There is an urgent need for patients with MMR proficient (pMMR) tumors. Oncolytic immunotherapy represents a novel therapeutic platform for the treatment of cancer with unique activity compared to conventional chemotherapy. The trial is to evaluate if the combination of Pexa-Vec oncolytic virus (PV) with immune checkpoint inhibition enhance antitumor immunity. Methods: Patients with microsatellite-stable and MSI-H mCRC refractory to PD-1 monotherapy were enrolled. Patients received either Arm A treated with PV + Durvalumab or Arm B with PV + Durvalumab and Tremelimumab. Each arm had two dose levels (DL) of PV, 3 x 108 pfu in DL1 and at 109 pfu in DL2, every 2 weeks for total 4 doses. The first dose of PV was administered on Day -12, followed by three more dose administration on Days 2, 16 and 30 in combination with the immune checkpoint inhibition. The primary endpoint is response rate, safety, tolerability and feasibility of these combination therapy in refractory metastatic CRC. Results: Here we report the safety data of Arm A.A total of 9 patients was enrolled so far. The longest follow-up time is 8 months. Four patients received DL1 PV and subsequent five patients received DL2 PV. No DLT was observed at the time of this abstract. No grade 4-5 adverse event (AE) were observed. All patients experienced lymphopenia. All patients with DL2 developed fever, hypotension and papulopastular rashes and were successfully managed with antipyretics, fluid support and skin protection, respectively. The most frequent treatment-related AEs were lymphopenia (8 [100%], fever (7 [87.5%]), chills (6 [75.0%]), hypotension (5 [62.5%]), papulopastular rashes (5 [62.5%], flu-like symptoms (2 [12.5%]), Nausea/vomiting (2 [12.5%]). Conclusions: Pexa-Vec in combination with Durvalumab showed a favorable safety profile. Clinical trial information: NCT03206073.

TPS4656 Background: Treatment options for advanced hepatocellular carcinoma (HCC) and liver dominant metastatic disease from colorectal or pancreatic cancers are limited with poor overall survival. Tadalafil has shown to increase anti-tumor immunity by decreasing myeloid derived suppressor cells (MDSC) and impair tumor growth in preclinical HCC models. Oral vancomycin affects bile acid metabolizing gut commensal bacteria leading to increased CXCL16 expression in the liver resulting in NKT mediated liver-selective anti-tumor effects. This study combines immune checkpoint inhibition (ICI) treatment with nivolumab in combination with tadalafil and oral vancomycin. We aim to evaluate the synergy of the antitumor effect induced by the change in gut microbiome with oral vancomycin and the immunomodulatory effect of PDE5 inhibition combined with ICI with nivolumab in advanced liver cancer or liver metastasis. Correlative Studies: Paired liver tumor biopsies are analyzed for genomic analysis (WES, RNA-seq), immune cell infiltration, proteomics and metabolomic studies (bile acids) and chemokine expression. Stool samples are analyzed for microbiota. Blood samples are analyzed for immune monitoring, cytokine profiles and pharmacokinetics of study drugs. Serum bile acid levels are determined in blood in the 2 hour period after test meal ingestion. Methods: This is a single-arm study of nivolumab, oral vancomycin and tadalafil. Treatment is delivered in 4-week cycles (C) and continues until off treatment. Imaging is done every 8 weeks. Biopsies are done at baseline and during week 3 of C2. Nivolumab is administered on day (D)1 of each C at a dose of 480 mg IV. Tadalafil is administered orally (PO); 10 mg daily starting on D1 of C1 and continues daily until off study. Vancomycin administration starts on D1 of C1 at 125 mg PO every 6 hours for a total daily dose of 500 mg. Patients will be on vancomycin 3 weeks on, 1 week off per regimen. The study is currently enrolling without DLT. Clinical trial information: NCT03785210 .

192 Background: Chemotherapy in aPDAC has resulted in only modest improvements in outcome. The effectiveness of ICI monotherapy is also limited in PDAC, suggesting an immunogenic inert tumor microenvironment. SBRT is safe and effective in locally advanced PDAC and exhibits enhanced antitumor immunity. We hypothesize that ICI plus SBRT will improves immunomodulatory effects of ICI in patients with aPDAC resulting in a greater clinical benefit. Methods: Eligible patients with aPDAC were enrolled to four different treatment cohorts. Cohort 1: Durvalumab (Durva) 1500 mg every 4 weeks + SBRT 1 fraction x 8Gy on day 1. Cohort 2: SBRT 5 fractions x 5Gy followed by Durva. Cohort 3: Durva + Tremelimumab (Treme) 75 mg every 4 weeks + SBRT 1 fraction x 8Gy on day 1. Cohort 4: SBRT 5 fractions x 5Gy followed by Durva + Treme. This was continued until unacceptable toxicity or progression of disease. A biopsy was performed at baseline and pre-cycle 2 of treatment for exploratory correlative analysis. The primary objective was to evaluate the safety and feasibility of combining ICI and SBRT to enhance the efficacy of ICI. Results: 51 patients with aPDAC were enrolled and 31 patients were evaluable for the efficacy. The most commonly TRAEs were lymphopenia. Grade 3-4 AEs were lymphopenia and anemia. No dose limiting toxicities were seen. Out of total 31 evaluable patients, 1 patient achieved a confirmed partial response seen in Cohort 1 and 2 patients in Cohort 4, and 7 stable disease across the 4 treatment arms. Median PFS and OS was 1.7 months (95% CI 0.7-2.8 months) and 3.4 months (95% CI 0.9-11.4 months) in cohort 1; 2.6 months (95% CI 2.1-4.7 months) and 9.1 months (95% CI 3.4-18.7 months)in cohort 2; 1.6 months (95% CI 0.5-4.0 months) and 3.0 months (95% CI 0.7-6.6 months) in cohort 3; and 3.2 months (95% CI 1.5-16.5months) and 6.4 months (95% CI 1.5-17.6 months) in cohort 4. Conclusions: The combination of ICI and SBRT is safe and well tolerated in patients with aPDAC. The overall response rate of 9.6% including 2 patients who achieved a durable partial response lasting over 12 months, suggests meaningful clinical activity. This signifies that ICI and SBRT is a potential new treatment for aPDAC. Clinical trial information: NCT02311361.