Patients with RAS wild-type right-sided unresectable liver-confined mCRC also benefit from cetuximab plus chemotherapy in first-line treatment.

: Growing evidence indicates that primary tumor location of metastatic colorectal cancer (mCRC) can affect response to specific therapy. This study aimed to assess the impact of primary tumor location on efficacy of cetuximab in Chinese patients with mCRC. We included patients with RAS wild-type liver-limited mCRC treated with first-line cetuximab plus chemotherapy or chemotherapy alone between June 2008 and December 2016. All patients were categorized as having left-sided tumors or right-sided tumors. Progression free survival (PFS), overall survival (OS), objective response rate (ORR) and conversion rate of surgery for liver metastases was analyzed according to tumor location and treatment. Right-sided tumors were characterized with larger primary tumor, poorer differentiation, more lymph node metastases and larger and more liver metastases. For patients with left-sided tumors (N=233), addition of cetuximab to chemotherapy significantly improved ORR (68.9% vs. 30.6%, OR=5.01, P < 0.001), conversion rate of liver surgery (33.5% vs. 10.8%, OR=4.18, P < 0.001), PFS (12.1 months vs. 6.1 months, HR=0.42, P < 0.001), and OS (not evaluable vs. 23.1 months, HR=0.31, P < 0.001). Among patients with right-sided tumors (N=85), cetuximab plus chemotherapy, compared with chemotherapy alone, also significantly improved ORR (56.8% vs. 29.3%, OR=3.18, P=0.010), PFS (9.3 months vs. 5.1 months, OR=0.57, P=0.012) and OS (25.3 months vs. 16.8 months, HR=0.56, P=0.032) but conversion rate of liver surgery (20.5% vs. 9.8%, HR=2.38, P=0.171). Our results demonstrated differential effect of cetuximab on efficacy outcomes based on tumor sidedness. Also, we found that patients with right-sided tumors also benefit from cetuximab plus chemotherapy but not as great as left-sided tumors and in general, did worse. In conclusion, findings of previous studies about differential effect of anti-EGFR therapy based on tumor sidedness are applicable to an Asian population.