title: The identification of incident cancers in UK primary care databases: a systematic review.
abstract: OBJECTIVE
  UK primary care databases are frequently used in observational studies with cancer outcomes. We aimed to systematically review methods used by such studies to identify and validate incident cancers of the breast, colorectum, and prostate.
  
  
  METHODS
  Medline and Embase (1980-2013) were searched for UK primary care database studies with incident breast, colorectal, or prostate cancer outcomes. Data on the methods used for case ascertainment were extracted and summarised. Questionnaires were sent to corresponding authors to obtain details about case ascertainment.
  
  
  RESULTS
  Eighty-four studies of breast (n = 51), colorectal (n = 54), and prostate cancer (n = 31) were identified; 30 examined >1 cancer type. Among the 84 studies, 57 defined cancers using only diagnosis codes, while 27 required further evidence such as chemotherapy. Few studies described methods used to create cancer code lists (n = 5); or made lists available directly (n = 5). Twenty-eight code lists were received on request from study authors. All included malignant neoplasm diagnosis codes, but there was considerable variation in the specific codes included which was not explained by coding dictionary changes. Code lists also varied in terms of other types of codes included, such as in-situ, cancer morphology, history of cancer, and secondary/suspected/borderline cancer codes.
  
  
  CONCLUSIONS
  In UK primary care database studies, methods for identifying breast, colorectal, and prostate cancers were often unclear. Code lists were often unavailable, and where provided, we observed variation in the individual codes and types of codes included. Clearer reporting of methods and publication of code lists would improve transparency and reproducibility of studies.
authors.affiliation: Department of Non-Communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Rañopa
authors.forename: Ian
authors.initials: I
authors.lastname: Douglas
authors.forename: Tjeerd
authors.initials: T
authors.lastname: van Staa
authors.forename: Liam
authors.initials: L
authors.lastname: Smeeth
authors.forename: Olaf
authors.initials: O
authors.lastname: Klungel
authors.forename: Robert
authors.initials: R
authors.lastname: Reynolds
authors.forename: Krishnan
authors.initials: K
authors.lastname: Bhaskaran
mesh_terms: D001943:Breast Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D015179:Colorectal Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D016208:Databases, Factual / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D011320:Primary Health Care / Q000379:methods* / Q000706:statistics & numerical data; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D006113:United Kingdom / Q000453:epidemiology
keywords: Read code; cancer; case identification; neoplasm; pharmacoepidemiology; primary care database