Study design setting

This was a nested case-control study using the QResearch database (version 44), an extensive, validated, anonymised primary care database comprising records of >35 million patients registered in approximately 1500 GP surgeries, spread throughout the UK, which have been using the EMIS System since 1989. The population in the QResearch database is representative of the UK population. Patients’ records have been linked with cancer registries, Office for National Statistics (ONS) mortality records, and Hospital Episode Statistics (HES). The cancer registration data include information on the date of diagnosis, type and location of the tumour, morphology, grade and stage, and treatment.