Distance from the anal verge as an indirect measure to predict response to anti-EGFR therapy in left side metastatic colon cancer

e15153 Background: Right and left sided colon cancers (RC, LC) differ with respect to biology and response to therapy. Several retrospective analyses have assessed the clinical effect of epidermal growth fator receptor (EGFR) targeted agents in patients with metastatic CRC (mCRC) according to the primary tumor location. Differentiating only right from left. But can in the LC responses differ according to the distance from the anal verge (DAV)? Methods: Exploratory retrospective analyses was planned to evaluate if LC responses differ according to the DAV. LC was defined as tumors originating anywhere from the distal rectum to the left colic flexure (splenic flexure). DAV was describe in cm measured by previous to surgery or treatment, colonoscopy, CT or MRI. Patients were divided for analysis purposes in two groups: Group A (tumors above 12cm from de anal verge), Group B (tumors below 12cm from the anal verge). Results: We retrospectively evaluated 29 patients with left metastatic colorectal cancer treated with anti-EGFR therapy as part of their treatment at the Paulistano Hospital -São Paulo from 2011 to 2018. Median population age 51.8 years (48.5-62.3). Median DAV 14.5 (4.6-25 cm). Median follow-up 12.8 months. No significant difference on stable and partial response rate was detected (Group A 43.7% vs Gropup B 56.3%), p=0.211. Long-rank test with a median pFS 8,5 meses and a PFS at 6 months of 66.7 vs 78,8 (Group A and Group B respectively ), p=0.901. Two-year OS was 58.4 % in Group A and 100% in Group B, p=0.17. Conclusions: Although no significant diferences were detected, responses rates were numerically higher in patients with tumors located below 12 cm from the anal verge. Further studies are needed to evaluate the association between response and DAV.