Cetuximab (C225), an anti-Epidermal Growth Factor receptor (EGFR) monoclonal antibody, has been widely used as a routine treatment for patients with metastatic colorectal cancer (mCRC); However, many patients who initially respond to cetuximab acquire resistance. The purpose of this study was to characterize new mechanism of acquired Cetuximab resistance. Firstly, tissue microarrays (TMA) comprising 191 CRC patients was constructed to evaluate the expression of chemokine receptor 7 (CCR7) by using immunohistochemistry (IHC). In CRC tumor tissues, CCR7 was significantly over-expressed compared with paired normal tissues (P < 0.001), and correlated with the infiltration depth (P = 0.03) and the regional lymph node metastasis (P = 0.006). Significant differences were also found in forms of overall survival (OS) and disease-free survival (DFS) between normal and tumor tissues (P < 0.001). More interestingly, EGFR was also highly expressed and co-localized with CCR7 in the tumor tissues from the patients who were insensitive to Cetuximab treatment. Secondly, we further explored the relationship between CCR7 expression and Cetuximab resistance by two CCR7 positive CRC cell lines, Caco-2 with wild-type KRAS (KRAS^wt ) and HCT116 with mutated KRAS (KRAS^G13D ). By the treatment of secondary lymphoid tissue chemokine (SLC, an exogenous high-affinity legend of CCR7), the inhibition rate of Cetuximab significantly decreased in both cells. Furthermore, the activation of SLC/CCR7 axis promoted epithelial mesenchymal transformation (EMT) in CRC tumor cells by increasing the expression of Twist and β-catenin. By using of CCR7 neutralizing antibody and p-AKT inhibitor rescued the above effects. These findings suggested that CCR7 was a key factor in those CRC patients, who have poorer reaction to Cetuximab. So combined inhibition of CCR7 and p-AKT will represent a rational therapeutic strategy for Cetuximab resistance patients.

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