Limitations
This study has some limitations. The reason for improved OS after treatment failure over time cannot be stated with certainty based on our data because we cannot provide detailed information on individual salvage strategies. Nevertheless, we tried to address potential biases. First, time to treatment failure was not significantly different in the 3 trials; hence, the notion that modern surveillance programs could have led to earlier detection of treatment failure and an earlier start of salvage therapy is not valid. Nevertheless, our findings that the relative risk of experiencing an LR as treatment failure increased in the third and fourth year of follow-up could have implications in the context of surveillance programs. Currently, the German guideline recommends proctoscopy and/or colonoscopy after surgery only up to 24 months, but not thereafter, which might need adaptation in the future.