title: Cancer-specific administrative data-based comorbidity indices provided valid alternative to Charlson and National Cancer Institute Indices.
abstract: OBJECTIVE
  We aimed to develop and validate administrative data-based comorbidity indices for a range of cancer types that included all relevant concomitant conditions.
  
  
  METHODS
  Patients diagnosed with colorectal, breast, gynecological, upper gastrointestinal, or urological cancers identified from the National Cancer Registry between July 1, 2006 and June 30, 2008 for the development cohort (n=14,096) and July 1, 2008 to December 31, 2009 for the validation cohort (n=11,014) were identified. A total of 50 conditions were identified using hospital discharge data before cancer diagnosis. Five site-specific indices and a combined site index were developed, with conditions weighted according to their log hazard ratios from age- and stage-adjusted Cox regression models with noncancer death as the outcome. We compared the performance of these indices (the C3 indices) with the Charlson and National Cancer Institute (NCI) comorbidity indices.
  
  
  RESULTS
  The correlation between the Charlson and C3 index scores ranged between 0.61 and 0.78. The C3 index outperformed the Charlson and NCI indices for all sites combined, colorectal, and upper gastrointestinal cancer, performing similarly for urological, breast, and gynecological cancers.
  
  
  CONCLUSIONS
  The C3 indices provide a valid alternative to measuring comorbidity in cancer populations, in some cases providing a modest improvement over other indices.
authors.affiliation: Department of Public Health, School of Medicine and Health Sciences, University of Otago, PO Box 7343, Wellington South, Wellington 6022, New Zealand. Electronic address: diana.sarfati@otago.ac.nz.
authors.forename: Diana
authors.initials: D
authors.lastname: Sarfati
authors.affiliation: Department of Public Health, School of Medicine and Health Sciences, University of Otago, PO Box 7343, Wellington South, Wellington 6022, New Zealand.
authors.forename: Jason
authors.initials: J
authors.lastname: Gurney
authors.affiliation: Department of Public Health, School of Medicine and Health Sciences, University of Otago, PO Box 7343, Wellington South, Wellington 6022, New Zealand.
authors.forename: James
authors.initials: J
authors.lastname: Stanley
authors.affiliation: Retired.
authors.forename: Clare
authors.initials: C
authors.lastname: Salmond
authors.affiliation: Faculty of Health Sciences, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
authors.forename: Peter
authors.initials: P
authors.lastname: Crampton
authors.affiliation: Department of Surgery and Anaesthesia, School of Medicine and Health Sciences, University of Otago, PO Box 7343, Wellington South, Wellington 6022, New Zealand.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Dennett
authors.affiliation: Department of Surgery, North Shore Hospital, Waitemata District Health Board, Private Bag 93-503 Takapuna, Auckland 0740, New Zealand.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Koea
authors.affiliation: Centre for Public Health Research, Massey University, PO Box 756, Wellington 6022, New Zealand; Department of Medical Statistics, London School of Hygiene and Tropical Medicine, Keppell Street, Bloomsbury, London WC1E7HT, UK.
authors.forename: Neil
authors.initials: N
authors.lastname: Pearce
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D015897:Comorbidity; D016208:Databases, Factual; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D054547:National Cancer Institute (U.S.); D009369:Neoplasms / Q000453:epidemiology*; D012042:Registries; D015203:Reproducibility of Results; D014481:United States / Q000453:epidemiology
keywords: Cancer; Comorbidity; Indices; Measurement; Multimorbidity; Validity