title: The effect of comorbidity on the use of adjuvant chemotherapy and survival from colon cancer: a retrospective cohort study.
abstract: BACKGROUND
  Comorbidity has a well documented detrimental effect on cancer survival. However it is difficult to disentangle the direct effects of comorbidity on survival from indirect effects via the influence of comorbidity on treatment choice. This study aimed to assess the impact of comorbidity on colon cancer patient survival, the effect of comorbidity on treatment choices for these patients, and the impact of this on survival among those with comorbidity.
  
  
  METHODS
  This retrospective cohort study reviewed 589 New Zealanders diagnosed with colon cancer in 1996-2003, followed until the end of 2005. Clinical and outcome data were obtained from clinical records and the national mortality database. Cox proportional hazards and logistic regression models were used to assess the impact of comorbidity on cancer specific and all-cause survival, the effect of comorbidity on chemotherapy recommendations for stage III patients, and the impact of this on survival among those with comorbidity.
  
  
  RESULTS
  After adjusting for age, sex, ethnicity, area deprivation, smoking, stage, grade and site of disease, higher Charlson comorbidity score was associated with poorer all-cause survival (HR = 2.63 95%CI:1.82-3.81 for Charlson score > or = 3 compared with 0). Comorbidity count and several individual conditions were significantly related to poorer all-cause survival. A similar, but less marked effect was seen for cancer specific survival. Among patients with stage III colon cancer, those with a Charlson score > or = 3 compared with 0 were less likely to be offered chemotherapy (19% compared with 84%) despite such therapy being associated with around a 60% reduction in excess mortality for both all-cause and cancer specific survival in these patients.
  
  
  CONCLUSIONS
  Comorbidity impacts on colon cancer survival thorough both physiological burden of disease and its impact on treatment choices. Some patients with comorbidity may forego chemotherapy unnecessarily, increasing avoidable cancer mortality.
authors.affiliation: Department of Public Health, University of Otago Wellington, PO Box 7343, Wellington 6242, New Zealand. diana.sarfati@otago.ac.nz
authors.forename: Diana
authors.initials: D
authors.lastname: Sarfati
authors.forename: Sarah
authors.initials: S
authors.lastname: Hill
authors.forename: Tony
authors.initials: T
authors.lastname: Blakely
authors.forename: Bridget
authors.initials: B
authors.lastname: Robson
authors.forename: Gordon
authors.initials: G
authors.lastname: Purdie
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Dennett
authors.forename: Donna
authors.initials: D
authors.lastname: Cormack
authors.forename: Kevin
authors.initials: K
authors.lastname: Dew
mesh_terms: D000328:Adult; D000368:Aged; D002423:Cause of Death; D017024:Chemotherapy, Adjuvant; D015331:Cohort Studies; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000453:epidemiology* / Q000401:mortality; D015897:Comorbidity; D005260:Female; D006331:Heart Diseases / Q000453:epidemiology; D006801:Humans; D007674:Kidney Diseases / Q000453:epidemiology; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D009369:Neoplasms / Q000453:epidemiology; D009520:New Zealand / Q000453:epidemiology; D016016:Proportional Hazards Models; D012042:Registries / Q000706:statistics & numerical data; D012189:Retrospective Studies; D016019:Survival Analysis; D015996:Survival Rate