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We would like to thank Dr Boffetta for his comment on potential overlaps in the selection of cohorts. As we tried to keep the principle of examining all the available publications in the systematic review and avoiding the double count in the meta-analysis, we have re-examined the materials of the study again. Even though different aspects in the follow-ups of five cohorts were noted in the original review of 12 studies, we agree with Dr Boffetta that, on re-examination, there …
Contributors KK and KEZ reviewed the relevant articles. KK analysed the data and drafted the manuscript. DP interpreted the data and revised the manuscript. All authors read and approved the final manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; internally peer reviewed.
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