title: Flexible statistical models provided new insights into the role of quantitative prognostic factors for mortality in gastric cancer.
abstract: OBJECTIVE
  To reassess the effects of prognostic factors on mortality in gastric cancers, and to illustrate the advantages of flexible modeling.
  
  
  METHODS
  A prospective population-based cohort of persons diagnosed with gastric cancers in 1976 to 1995 in Burgundy, France, was followed for 5 years since diagnosis. Multivariable survival analyses, stratified by cancer stage, involved both conventional Cox's model and its flexible generalization, which permitted testing the underlying assumptions and accounting for changes over time in the effects of prognostic factors.
  
  
  RESULTS
  Conventional assumptions of proportional hazards (PH) (P=0.003) and linear increase in risk with increasing age (P=0.003) were rejected for age at cancer diagnosis in patients with less advanced (stage I/II) gastric cancers. Flexible modeling revealed that: (1) the effect of age was important mostly in the first year after diagnosis; and (2) mortality increased both for the youngest and the oldest patients. In conventional analyses, calendar year of diagnosis had no association with mortality in stage I/II cancers (P=0.37). In contrast, flexible analyses indicated a statistically significant reduction in early, mostly postsurgical, mortality between early 1970s and 1980s.
  
  
  CONCLUSIONS
  Flexible modeling and testing conventional assumptions may yield new insights in prognostic studies of cancer mortality.
authors.affiliation: Inserm, U866, Dijon, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Binquet
authors.forename: Michal
authors.initials: M
authors.lastname: Abrahamowicz
authors.forename: Karine
authors.initials: K
authors.lastname: Astruc
authors.forename: Jean
authors.initials: J
authors.lastname: Faivre
authors.forename: Claire
authors.initials: C
authors.lastname: Bonithon-Kopp
authors.forename: Catherine
authors.initials: C
authors.lastname: Quantin
mesh_terms: D000367:Age Factors; D000368:Aged; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009367:Neoplasm Staging; D011379:Prognosis; D016016:Proportional Hazards Models; D011446:Prospective Studies; D013274:Stomach Neoplasms / Q000401:mortality*; D016019:Survival Analysis