Abstract 485: Early antibiotic exposure delays disease progression following immune checkpoint inhibitor therapy for hepatocellular carcinoma: Evidence from an observational study

<jats:title>Abstract</jats:title> <jats:p>Background: Immune checkpoint inhibition (ICI) is an expanding option in hepatocellular carcinoma (HCC). Antibiotics (ATB) have been shown to reduce response and survival after ICI in other cancers.</jats:p> <jats:p>Methods: Efficacy of ICI is described in patients (pt) from 11 centres (246 USA, 100 Asia, 68 Europe), with median overall (OS), progression-free survival (PFS) and best response (RECIST 1.1) compared between pt with and without ATB exposure in the early immunotherapy period (EIOP) of 30 days before and after ICI initiation.</jats:p> <jats:p>Results: Most of our 414 pt were cirrhotic (297, 71.7%) due to hepatitis C (162, 391.1%) with Barcelona Clinic Stage C (294, 71.0%), Child-Pugh class (CP) A (313, 76.3%) and AFP&gt;400 IU/mL (158, 39.3%). OS was 15.4 mo (95%CI 13.1-17.7) and PFS was 5.3 months (95% CI 4.5-6.0). Most ICI was anti-PD-1 monotherapy (358, 86.5%) and given as 1st (173, 41.8%) or 2nd line (208, 50.2%). Best response to ICI was complete response in 27 pt (6.5%), partial response in 45 (10.9%), stable disease (SD) in 160 (38.6%) and progressive disease (PD) in 161 (38.9%). ATB was given to 167 pt (40.3%), prior to or early after (30 d) ICI initiation (EIOP, 157, 38.0%) or beyond 30 days (21, 5.1%), mostly as beta-lactams (27, 10.9%) or quinolones (26, 10.5%). ATB use was independent of CP class (p=0.76), ECOG performance status (p=0.58) and BCLC stage (p=0.60). mOS in the EIOP+ group was similar to the EIOP- group (13.1 vs 15.5 mo, p=0.92). mPFS in the EIOP+ group was significantly longer than the EIOP- group (7.9 vs 4.2 mo, p=0.004). Observations persisted when stratified by CP class (p=0.42) and ICI type (p=0.92). Partial response rate was higher in the EIOP+ group (17.3% vs 8.6%, p=0.01), although overall objective response and disease control rates were similar between EIOP groups (ORR: 22.7% vs 15.9%, p=0.10; DCR: 64.0% vs 56.6%, p=0.15). Pt in the EIOP+ group were not more likely to experience gastrointestinal AE (EIOP +/- 9.2%/5.4%, p=0.12) or hepatic AE (EIOP +/-, 17.9%/16.5%, p=0.92) of any grade, while severe liver AE (grade 2 or above) were less common in the EIOP+ group (EIOP+/- 2.8%/9.5%, p=0.01).</jats:p> <jats:p>Conclusions: ATB in the 30 d before or after ICI initiation in HCC is associated with prolonged PFS. This is contrary to findings in other solid tumors. Evaluation of the immune-microbiologic determinants of response to ICI in HCC a key research question.</jats:p> <jats:p>Citation Format: Petros Fessas, Muntaha Naeem, Thomas U. Marron, David Szafron, Elad Sharon, Anwar Saeed, Tomi Jun, Sirish Dharmapuri, Abdul R. Naqash, Thoetchai Peeraphatdit, Anuhya Gampa, Yinghong Wang, Uqba Khan, Mahvish Muzaffar, Musharraf Navaid, ChiehJu Lee, Pei-Chang Lee, Anushi Bulumulle, Bo Yu, Sonal Paul, Neil Nimkar, Dominik Bettinger, Hannah Hildebrand, Yehia I. Abugabal, Tiziana Pressiani, Nicola Personeni, Naoshi Nishida, Masatoshi Kudo, Ahmed Kaseb, Yi-Hsiang Huang, Celina Ang, Anjana Pillai, Lorenza Rimassa, David J. Pinato. Early antibiotic exposure delays disease progression following immune checkpoint inhibitor therapy for hepatocellular carcinoma: Evidence from an observational study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 485.</jats:p>