Abstract
BACKGROUND: Rectal cancer is characterized by more local recurrence (LR) and lung metastasis than colon cancer. However, the diagnosis of rectal cancer is not standardized as there is no global consensus on its definition and classification. The classification of rectal cancer differs between Japanese and Western guidelines. AIM: To clarify the characteristics of rectal cancer by comparing the tumor location and characteristics of rectal cancer with those of colon cancer according to each set of guidelines. METHODS: A total of 958 patients with Stage II and III colorectal cancer were included in the analysis: 607 with colon cancer and 351 with rectal cancer. Localization of rectal cancers was assessed by enema examination and rigid endoscopy. According to Japan guidelines, rectal cancer is classified as Rb (below the peritoneal inversion), Ra (between the inferior margin of second sacral vertebrae and Rb) or RS (between Ra and sacral promontory). RESULTS: There were no significant differences between RS rectal cancer and colon cancer in the rates of liver and lung metastasis or LR. Lung metastasis and LR were significantly more common among Rb rectal cancer (in Japan) than in colon cancer (P = 0.0043 and P = 0.0002, respectively). Lung metastases and LR occurred at significantly higher rates in rectal cancer measuring ≤ 12 cm and ≤ 10 cm than in colon cancers (P = 0.0117, P = 0.0467, P = 0.0036, P = 0.0010). Finally, the rates of liver metastasis, lung metastasis, and LR in rectal cancers measuring 11 cm to 15 cm were 6.9%, 2.8%, and 5.7%, respectively. These were equivalent to the rates in colon cancer. CONCLUSION: High rectal cancer may be treated with the same treatment strategies as colon cancer. There was no difference in the classification of colorectal cancer between Japan and Western countries.