How alarm symptoms for PDAC overlap with other conditions has rarely been evaluated, and it is unclear if there are certain symptoms or combinations of symptoms that are unique to PDAC. In addition, very little is known about what features of the disease prompt GPs to suspect cancer and initiate

investigations moreover and referrals. Current National Institute for Health and Care Excellence (NICE) referral guidelines for suspected cancer in primary care contain limited specific information on the best method for referring patients with suspected PDAC or BTC for further investigation, but new guidelines are underway.14 The primary aim of this study was therefore to determine the early symptom profiles of PDAC and BTC in a large primary care cohort. Secondary aims include comparing early symptom trends between BTC and PDAC, defining

symptom onset in PDAC and evaluating trends in routine blood tests nearest to the time of diagnosis. Methods Data source In the UK most GPs record patient data electronically. A subset of GP practices have opted to provide anonymous electronic patient records for use in clinical and epidemiological research. The Health Improvement Network (THIN) is a primary care database, which includes more than 11 million electronic patient records, from 562 GP practices, covering around 6% of the UK population (http://csdmruk.cegedim.com/). The data are broadly representative of the UK general practice population in terms of demographics and consultation behaviour.15 16 Diagnoses, symptoms and referrals to secondary care are electronically recorded using the Read code system.17 Clinical diagnoses recorded by GPs electronically have recently been shown to be accurate compared with other reliable sources.16 18 All drug prescriptions and variables such as body mass index (BMI), blood pressure, smoking status, alcohol intake and laboratory results are also recorded. Study design A case–control design was used to compare ‘alarm’ symptoms and commonly performed blood test results in patients with a diagnosis of PDAC

or BTC. Unaffected controls were matched for age, sex, practice and year of diagnosis. Study population All patients with a Read code diagnosis of PDAC or BTC between 1 January 2000 and 31 December 2010 were extracted from the database. Read code lists to identify Drug_discovery diagnosed patients were developed using previously described methodology.19 The date of diagnosis was set as the index date and for control patients a random consultation date was selected to become the index date. All patients were required to have contributed 2 years of data prior to the index date. Two years was selected as the time period of interest based on preliminary data suggesting alarm symptoms were uncommon beyond this time period (figure 1A, B).