Primary Tumor Location As a Prognostic and Predictive Factor in Metastatic Colorectal Cancer (mcrc) Treated with Chemotherapy Plus Cetuximab: A Retrospective Analysis.

711 Background: Left- and right-sided colon cancers are significantly different in epidemiologic, clinicopathological and molecular characteristics. However, the impact of primary tumor location in mCRC treated biological targeted agent in combination with chemotherapy is unclear. We therefore investigated the prognostic and predictive impact of primary tumor location in mCRC. Methods: Single-institution, retrospective, case-control study was reviewed. A total of 96 patients with mCRC were enrolled between January 2011 and December 2015. We evaluated the association between tumor location and survival parameters in patients with previously untreated mCRC receiving first-line chemotherapy plus cetuximab or bevacizumab. The impact of primary tumor location for cetuximab and bevacizumab groups was analyzed, respectively. Left-sided primary tumors were defined as tumors from rectum to splenic flexure, while right-sided primary tumors were defined as tumors from cecum to the distal part of the transverse colon. Results: 68 patients presented left-sided tumors and 28 patients right-sided primary tumors. In the cetuximab group, left-sided tumors were significantly superior to right-sided tumors in terms of the progression-free survival (PFS) and Overall survival (OS) (PFS, left vs right, 18.3 vs 6.8 M, p = 0.0415; OS, 50.6 vs10.5 M, p = 0.0004). Likewise, in the bevacizumab group, OS showed differences between the left- and right-sided tumors (PFS, left vs right, 11.6 vs 7.3 M, p = 0.1904; OS, 25.7 vs 16.2 M, p = 0.0389). In left-sided tumors, cetuximab group were significantly superior to bevacizumab group in terms of the OS (PFS, cetuximab vs bevacizumab, 18.0 vs 11.6 M, p = 0.1088; OS, 50.6 vs 25.7 m p = 0.0354). Conversely, in right-sided, the survival times showed no differences between cetuximab- and bevacizumab group (PFS, cetuximab vs bevacizumab, 6.8 vs 7.3 M, p = 0.7816; OS, 10.5 vs 16.2 M, p = 0.1088). Conclusions: Our study demonstrates that primary tumor location is an important prognostic factor in previously untreated mCRC. Furthermore, left-sided primary tumor location might be a strong predictor of PFS and OS in cetuximab therapy.