title: Generalizability of cancer clinical trial results: prognostic differences between participants and nonparticipants.
abstract: BACKGROUND
  The generalizability of clinical trial results is questionable, because fewer than 5% of cancer patients participate. The authors examined the comparability of clinical trial participants and nonparticipants and the potential impact of differences.
  
  
  METHODS
  A retrospective cohort of 19,340 cancer patients who were diagnosed between January 1990 and December 1997 was characterized by trial participation. The distributions of prognostically important factors among trial participants were compared with the distributions among nonparticipants and the population of patients diagnosed during the same period in the Surveillance, Epidemiology, and End Results population. The impact of these factors on survival was examined by using a Cox proportional hazards analysis.
  
  
  RESULTS
  Trial participants were younger and had better performance status and fewer comorbid conditions compared with nonparticipants. However, participants were more likely to have locally advanced disease, positive lymph node status, poorly differentiated tumors, liver metastases, and multiple metastatic sites. The former factors were associated with significantly longer survival, whereas the later factors were associated with significantly shorter survival.
  
  
  CONCLUSIONS
  The lack of comparability between trial participants and nonparticipants called into question the generalizability of clinical trial results. Although selective recruitment for clinical trials is justified, the authors encourage the use of population-based trials of effectiveness in "all comers."
authors.affiliation: Department of Biostatistics and Applied Mathematics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA. lelting@mdanderson.org
authors.forename: Linda S
authors.initials: LS
authors.lastname: Elting
authors.forename: Catherine
authors.initials: C
authors.lastname: Cooksley
authors.forename: B Nebiyou
authors.initials: BN
authors.lastname: Bekele
authors.forename: Michael
authors.initials: M
authors.lastname: Frumovitz
authors.forename: Elenir B C
authors.initials: EB
authors.lastname: Avritscher
authors.forename: Charlotte
authors.initials: C
authors.lastname: Sun
authors.forename: Diane C
authors.initials: DC
authors.lastname: Bodurka
mesh_terms: D000328:Adult; D000368:Aged; D002986:Clinical Trials as Topic; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000175:diagnosis / Q000401:mortality; D010358:Patient Participation; D011379:Prognosis; D012189:Retrospective Studies; D018426:SEER Program; D015996:Survival Rate