// Jiang Chen 1, 2, * , Tong Ji 2, * , Jie Zhao 1, 2 , Gaofeng Li 2 , Jian Zhang 1 , Renan Jin 1 , Jinghua Liu 1 , Xiaolong Liu 1 , Xiao Liang 1 , Diyu Huang 1 , Anyong Xie 1, 3 , Hui Lin 1 , Yong Cang 2 , Xiujun Cai 1 1 Department of General Surgery, Sir Run Run Shaw Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, 310058, China 2 Life Sciences Institute and Innovation Center for Cell Signalling Network, Zhejiang University, Hangzhou, Zhejiang, 310029, China 3 Institute of Translational Medicine, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, 310029, China * These authors have contributed equally to this work Correspondence to: Xiujun Cai, e-mail: cxjzu@hotmail.com Yong Cang, e-mail: cangyong@zju.edu.cn Hui Lin, e-mail: 369369@zju.edu.cn Keywords: hepatocellular carcinoma(HCC), phosphorylated extracellular signaling-regulated kinase(pERK), programmed death receptor-1 (PD-1), sorafenib Received: December 25, 2015 Accepted: March 31, 2016 Published: April 25, 2016 ABSTRACT Sorafenib is a multikinase inhibitor approved as the first line treatment for late stage hepatocellular carcinoma (HCC). Due to its significant variation in clinical benefits among patients, defining prognostic biomarkers for sorafenib sensitivity in HCC would allow targeted treatment. Phosphorylated extracellular signaling-regulated kinase (pERK) was proposed to predict the response to sorafenib in HCC, but clinical supports are mixed or even contradictory. Here we found that pERK expression levels are variable in different nodules from individual patient liver. Xenografts derived from resected tumors are resistant to sorafenib inhibition when expressing low levels of pERK. This correlation of low pERK levels and sorafenib resistance is corroborated by histological characterization of chemical-induced and genetic mouse models for pERK-positive and pERK-negative HCC respectively, as well as computed tomography (CT) imaging of patient tumors with validated pERK expression. Mouse and human HCC samples expressing low pERK show strong inflammatory infiltrating cells and significant enrichment of intratumoral CD8 + cytotoxic T lymphocytes that express programmed death receptor-1 (PD-1). These pERK - PD-1 + patients have poorer overall and disease-free survival than pERK + PD-1 - patients. In conclusion, our data suggest that anti-PD-1 immunotherapy might complement sorafenib in treating HCC patients by targeting sorafenib-resistant cancer cells, and the dual pERK and PD-1 biomarkers would help HCC patient selection to achieve optimal clinical benefits.