title: Symptom lead time distribution in lung cancer: natural history and prospects for early diagnosis.
abstract: BACKGROUND
  Before their diagnosis, patients with cancer present in primary care more frequently than do matched controls. This has raised hopes that earlier investigation in primary care could lead to earlier stage at diagnosis.
  
  
  METHODS
  We re-analysed primary care symptom data collected from 247 lung cancer cases and 1235 matched controls in Devon, UK. We identified the most sensitive and specific definition of symptoms, and estimated its incidence in cases and controls prior to diagnosis. We estimated the symptom lead time (SLT) distribution (the time between symptoms attributable to cancer and diagnosis), taking account of the investigations already carried out in primary care. The impact of route of diagnosis on stage at diagnosis was also examined.
  
  
  RESULTS
  Symptom incidence in cases was higher than in controls 2 years before diagnosis, accelerating markedly in the last 6 months. The median SLT was under 3 months, with mean 5.3 months [95% credible interval (CrI) 4.5-6.1] and did not differ by stage at diagnosis. An earlier stage at diagnosis was observed in patients identified through chest X-ray originated in primary care.
  
  
  CONCLUSIONS
  Most symptoms preceded clinical diagnosis by only a few months. Symptom-based investigation would lengthen lead times and result in earlier stage at diagnosis in a small proportion of cases, but would be far less effective than standard screening targeted at smokers.
authors.affiliation: University of Bristol, School of Social and Community Medicine, Bristol, UK and University of Exeter Medical School, Exeter, UK t.ades@bristol.ac.uk.
authors.forename: Anthony E
authors.initials: AE
authors.lastname: Ades
authors.affiliation: University of Bristol, School of Social and Community Medicine, Bristol, UK and University of Exeter Medical School, Exeter, UK.
authors.forename: Mousumi
authors.initials: M
authors.lastname: Biswas
authors.affiliation: University of Bristol, School of Social and Community Medicine, Bristol, UK and University of Exeter Medical School, Exeter, UK.
authors.forename: Nicky J
authors.initials: NJ
authors.lastname: Welton
authors.affiliation: University of Bristol, School of Social and Community Medicine, Bristol, UK and University of Exeter Medical School, Exeter, UK.
authors.forename: William
authors.initials: W
authors.lastname: Hamilton
mesh_terms: D016022:Case-Control Studies; D002637:Chest Pain / Q000453:epidemiology*; D003371:Cough / Q000453:epidemiology*; D057210:Delayed Diagnosis / Q000517:prevention & control; D018450:Disease Progression; D004417:Dyspnea / Q000453:epidemiology*; D055088:Early Detection of Cancer; D004739:England / Q000453:epidemiology; D005221:Fatigue / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D008175:Lung Neoplasms / Q000175:diagnosis / Q000453:epidemiology* / Q000473:pathology; D009367:Neoplasm Staging; D012372:ROC Curve; D018570:Risk Assessment; D012907:Smoking / Q000453:epidemiology*; D013997:Time Factors; D015431:Weight Loss
keywords: Lung cancer; lead time; stage at diagnosis; symptom lead time