Appraisal of Prognostic Interaction between Sidedness and Mucinous Histology in Colon Cancer: A Population-Based Study Using Inverse Probability Propensity Score Weighting

Introduction: Colon cancer with different sidedness (right vs. left) and histology (mucinous vs. non-mucinous) may represent different disease entities. We investigated whether the prognostic values of sidedness and histology differed according to each other. Materials and Methods: We analyzed 81342 patients with stage II-IV colon cancer from the Surveillance, Epidemiology, and End Results database between 2004 and 2012. Patients were divided into four subgroups on the basis of sidedness and histology: non-mucinous right-sided, non-mucinous left-sided, mucinous right-sided, and mucinous left-sided subgroups. Among each tumor stage, median overall survival (mOS) was compared between these subgroups after inverse probability propensity score weighting to handle confounding factors. Results: In the stage IV subgroup, the prognosis for non-mucinous left-sided tumors (weighted mOS, 24.5 months) was significantly better than that for non-mucinous right-sided tumors (weighted mOS, 16.5 months; P<0.001) and that for mucinous left-sided tumors (weighted mOS, 16.5 months; P<0.001), whereas the survival was similar between left-sided and right-sided tumors with the mucinous subtype (weighted mOS, 16.5 months for both; P=0.570; test for interaction between sidedness and histology, P(interaction)<0.001), and between mucinous and non-mucinous tumors in the right-sided colon (weighted mOS, 16.5 months for both; P=0.207). Similar findings were detected in the stage III subgroup (P(interaction)<0.001). In the stage II subgroup, the survival was comparable among the four sidedness-histology subgroups (P=0.159 and P(interaction)=0.466). Conclusions: In stage III/IV colon cancer, the prognostic value of sidedness differed according to histology, and vice versa. By contrast, neither should be considered in risk stratification for stage II colon cancer.