Background: Previous studies of stage III colon cancer using the hazard function demonstrated that the risk of recurrence in patients with adjuvant chemotherapy never exceeded that of patients without adjuvant chemotherapy. However, it is unclear whether the same can be said for rectal cancer patients and whether adjuvant chemotherapy reduces recurrence. This study aimed to compare the recurrence hazard of stage III rectal cancer with that of colon cancer by adjuvant chemotherapy status using the hazard function, a method that allows for the assessment of instantaneous risk of recurrence over time. Methods: This retrospective nationwide study consisted of 10,356 patients with stage III colorectal cancer who underwent curative resection between January 1997 and December 2012 in Japan. Recurrence hazards of rectal and colon cancers were compared between patients treated with adjuvant chemotherapy and those who were not. Analyses in which recurrence was divided into local and distant recurrence were also performed. Results: The hazard rate of recurrence in rectal cancer patients with adjuvant chemotherapy was consistently lower throughout the follow-up period, and the peak time of recurrence later, compared to patients without adjuvant chemotherapy (peaked at 15.7 vs. 7.1 months). Adjuvant chemotherapy also strongly suppressed distant recurrence but not local recurrence in rectal cancer patients. Similar results were observed in colon cancer patients. Conclusions: Our results using nationwide real-world data in Japan suggest that, similar to what is observed in colon cancer patients, adjuvant chemotherapy delays the peak of recurrence and suppresses distant recurrence in stage III rectal cancer patients.
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