title: Conditional survival and the choice of conditioning set for patients with colon cancer: an analysis of NSABP trials C-03 through C-07.
abstract: OBJECTIVE
  Colon cancer overall survival (OS) is usually computed from the time of diagnosis. Survival gives the initial prognosis but does not reflect how prognosis changes with changing hazard rates over time. Conditional survival (probability of surviving y additional years given they have survived x years [CS or OS|OS]) is an alternative measure that accounts for elapsed time since diagnosis, providing more relevant prognostic information. We extend the concept of CS to condition on the set of patients alive, recurrence-free, and second primary cancer-free (disease-free survival [OS|DFS]).
  
  
  METHODS
  Using data from National Surgical Adjuvant Breast and Bowel Project trials C-03 through C-07, 5-year OS|DFS was calculated on patients who were disease free up to 5 years after diagnosis, stratified by age, stage, nodal status, and performance status (PS).
  
  
  RESULTS
  For stage II, OS|DFS improved from 87% to 92% at 5 years. For stage III, OS|DFS improved from 69% to 88%. Patients younger than 50 years showed OS|DFS improvement from 79% to 95%; those older than 70 years showed no sustained increase in OS|DFS. Node-negative patients with > or = 12 nodes resected showed little change (89% to 94%); those with more than four positive nodes showed an improvement (57% to 86%). Patients with a PS of 0 or 1 demonstrated a small improvement; those with a PS of 2 did not (64% to 58%).
  
  
  CONCLUSIONS
  Prognosis improves over time for almost all groups of patients with colon cancer, especially those with positive nodes. OS|DFS is a more relevant measure of prognosis for those who have already survived disease free a period of time after diagnosis.
authors.affiliation: Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA. zambonibx@carlow.edu
authors.forename: Beth A
authors.initials: BA
authors.lastname: Zamboni
authors.forename: Greg
authors.initials: G
authors.lastname: Yothers
authors.forename: Mehee
authors.initials: M
authors.lastname: Choi
authors.forename: Clifton D
authors.initials: CD
authors.lastname: Fuller
authors.forename: James J
authors.initials: JJ
authors.lastname: Dignam
authors.forename: Peter C
authors.initials: PC
authors.lastname: Raich
authors.forename: Charles R
authors.initials: CR
authors.lastname: Thomas
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Connell
authors.forename: Norman
authors.initials: N
authors.lastname: Wolmark
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Wang
mesh_terms: D000367:Age Factors; D000368:Aged; D017326:Clinical Trials, Phase III as Topic; D003110:Colonic Neoplasms / Q000175:diagnosis / Q000188:drug therapy / Q000401:mortality* / Q000473:pathology; D018572:Disease-Free Survival; D006801:Humans; D053208:Kaplan-Meier Estimate; D008207:Lymphatic Metastasis; D008875:Middle Aged; D011379:Prognosis; D016016:Proportional Hazards Models; D011785:Quality Assurance, Health Care / Q000379:methods; D016032:Randomized Controlled Trials as Topic; D016019:Survival Analysis; D014481:United States / Q000453:epidemiology
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