Funding for this research was provided by:
Cancer Research UK (C37316/A18225)
Received: 20 June 2017
Accepted: 19 December 2017
First Online: 19 January 2018
Ethical approval and consent to participate
: The CPRD Group has obtained ethical approval from a National Research Ethics Service Committee (NRECS) for all purely observational research using anonymised CPRD data.
: As the study had no direct patient involvement, patient consent for the study was not required.
: The authors declare that they have no competing interests.
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