BACKGROUND: This study evaluates the clinical characteristics of rectal cancer involving the anal canal. METHODS: A total of 346 consecutive patients with primary low rectal cancer located below the peritoneal reflection were reviewed in this study. Patients were divided into two groups according to whether the lower edge of the tumor came in contact with the anal canal (P group, n = 78) or not (Rb group, n = 268). Clinical and pathological parameters, recurrence rates, and survival rates were compared between the two groups. RESULTS: The occurrence of uncommon histological types of tumor was significantly higher in the P group than in the Rb group. P group patients also had a significantly higher lateral pelvic node metastasis rate (p < 0.001), lower 5-year overall survival rate (p = 0.0491), and higher 5-year local recurrence rate (p = 0.0171) than Rb group patients. Multivariate analysis revealed that tumor location was a significant risk factor for local recurrence. In the P group, multivariate analysis showed that uncommon histological tumor types were a significant prognostic factor. CONCLUSION: Rectal cancer involving the anal canal should be treated with special care, considering the particularly high lateral pelvic lymph node metastasis rate and high local recurrence rate.
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