Purpose Cancers which arise in the proximal and distal colon are suggested to be different clinically, pathologically, and genetically. The aim of this study is to clarify whether clinical behavior of colonic poorly differentiated adenocarcinoma, mucinous adenocarcinoma, and signet-cell carcinoma (Por/Muc/Sig cancers), minor and aggressive subpopulation in colonic cancers, differs in accordance with the tumor location. Methods A total of 3,175 patients with curatively resected colonic cancers were studied. Clinical and pathological features were compared between Por/Muc/Sig cancers and well or moderately differentiated adenocarcinomas (Wel/Mod cancers) and between proximal and distal cancers in each histologic type. Results Por/Muc/Sig cancers (n=213) were more advanced in the TNM stage and showed worse disease-specific survival than Wel/Mod cancers (n=2,692). In Por/Muc/Sig cancers, but not in Wel/Mod cancers, proximal cancers showed significantly better disease-specific survival than distal cancers (88.9% vs. 76.5%, p=0.0234), and a multivariate analysis showed that proximal tumor location was an independent predictor of fair prognosis (hazard ratio (HR), 0.458; 95% confidence interval (CI), 0.218-0.961; p=0.0390). In addition, female gender also was an independent predictor of fair prognosis in Por/Muc/Sig cancers (HR, 0.373; 95% CI, 0.151-0.922) and not in Wel/Mod cancers. Conclusions Proximal Por/Muc/Sig cancers were suggested to be a distinct subpopulation with a favorable oncologic outcome. Tumor location and gender might be helpful in the risk stratification after curative surgery for Por/Muc/Sig cancers.
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