[Correspondence] Uncovering causal clues in the development of second primary cancers – Authors’ reply

We thank Huan Yi and Jianguang Ji for their interest in our study about the cumulative incidence of second primary cancers in Danish cancer survivors.1 We acknowledge their concern about the relatively short overall follow-up time. Although survival has considerably improved for many cancers, large variations in survival among different cancer types contribute to the short overall follow-up time, as illustrated in figure 1 and the appendix (p 10) of our Article.1