title: The impact of patient comorbidity on cancer stage at diagnosis.
abstract: BACKGROUND
  It is known that cancer stage is affected by comorbidity, but the evidence regarding the magnitude and even direction of this effect is highly inconsistent and poorly understood. The aims of this study were to establish the impact of comorbidity on cancer stage at diagnosis, using both specific individual comorbid conditions and a global measure of comorbidity; and to assess whether this impact varied by cancer site, level of comorbidity burden and individual comorbidity type.
  
  
  METHODS
  We examined comorbidity among 14,096 patients with breast, colon, rectal, liver, stomach, ovarian, uterine, bladder or kidney cancer. Patients were identified from cancer registry data, and then linked to hospitalisation data to determine the presence of comorbidity in the 5 years preceding cancer diagnosis. Individual comorbid conditions were identified using ICD-10 codes, and overall burden of comorbidity attributed using a cancer-specific measure of comorbidity (C3 Index).
  
  
  RESULTS
  We observed that the presence of patient comorbidity (a) increases the odds of being diagnosed with distant metastases, (b) does not lead to earlier diagnosis and (c) increases the likelihood of a patient receiving no stage of disease at diagnosis.
  
  
  CONCLUSIONS
  Patient comorbidity has a substantial impact on cancer stage at diagnosis; however, this impact varies considerably by cancer type, individual comorbid condition and overall comorbidity burden.
authors.affiliation: Department of Public Health, University of Otago, PO Box 7343, Wellington, New Zealand.
authors.forename: Jason
authors.initials: J
authors.lastname: Gurney
authors.affiliation: Department of Public Health, University of Otago, PO Box 7343, Wellington, New Zealand.
authors.forename: Diana
authors.initials: D
authors.lastname: Sarfati
authors.affiliation: Department of Public Health, University of Otago, PO Box 7343, Wellington, New Zealand.
authors.forename: James
authors.initials: J
authors.lastname: Stanley
mesh_terms: D000328:Adult; D000368:Aged; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging / Q000379:methods; D009369:Neoplasms / Q000175:diagnosis* / Q000473:pathology*; D009520:New Zealand