Impact of adyuvant chemotherapy treatment according to tumor primary location in colorectal cancer: Experience at University Hospital Ramon y Cajal (HURyC) Madrid

655 Background: Adyuvant chemotherapy is a unified therapeutic principle in colon cancer (CC). However, many prognostic factors are arising to determine who really benefits from adyuvant chemotherapy in order to avoid overtreatment. Primary tumor location of CC is emerging as an important prognostic factor owing to distinct biological features. However, there is hardly any evidence showing the benefit of treatment according to primary tumor location. Methods: We retrospectively included patients with stage II and III CC that underwent surgical resection between 2009 and 2014 HURyC. We performed a multivariable Cox model analysis to estimate the benefit of chemotherapy according to tumor location in terms of DFS and OS. The model was further adjusted by including the following confounders: ECOG-PS, number of removed nodes ( < 12 or ≥ 12), use of adyuvant chemotherapy and age. A covariate was considered a confounder factor if the difference between the adjusted and unadjusted coefficient of chemotherapy varied > 10%. Stata 13.1 was used to analyze the data. Results: 564 patients were identified (267 left sided and 297 right sided). The median follow-up of the entire cohort was 49 months. Globally, chemotherapy did not improve DFS neither in right sided or left sided CC (HR: 0.81, p: 0.58; HR 1.31, p: 0.4, respectively). As for OS, it was improved when adding chemotherapy in both sides (right sided CC HR 0.51, p: 0.061 and left sided CC HR 0.42, p: 0.009). By stages, chemotherapy did not improve DFS or OS according to tumor localization in stage II. In right sided stage III, there was a trend to improve both DFS and OS (HR: 0.54, p: 0.14; HR: 0.39, p: 0.1, respectively). In left sided stage III, there was a trend to improve DFS (HR: 0.66, p: 0.36) and there was an improvement in OS (HR: 0.23, p < 0.001). Conclusions: The multivariable analysis showed benefit of chemotherapy in both right and left sided CC in terms of OS, exhibiting more benefit those patients with left sided CC.