title: Survival analysis of breast cancer patients using Cox and frailty models.
abstract: BACKGROUND
  Cox proportional hazard (CPH) model is the most widely used model for survival analysis. When there are unobserved/unmeasured individuals factor, then the results of the Cox proportional hazard model may not be reliable. The purpose of this study was to compare the results of CPH and frailty models in breast cancer (BC) patients.
  
  
  METHODS
  A historical cohort study was carried out using medical records gathered from the Fars Province Cancer Registry. The dataset consisted of 769 women having BC referred to Shiraz Namazi Hospital, south of Iran. These patients had been followed for 6 years. After selecting the most important prognostic risk factors on survival, CPH and gamma-frailty Cox models were used to estimate the effects of the risk factors.
  
  
  RESULTS
  The results of CPH model showed that, tumor characteristics and number of involved lymph nodes increase the mortality hazard of BC(P<0.05). In addition, the frailty model showed that there is at least a latent factor in the model (P=0.005).
  
  
  CONCLUSIONS
  Both of the frailty and CPH model emphasis that the early detection of BC improves survival in BC patients.
authors.affiliation: Department of Biostatistics & Epidemiology, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran. javad.faradmal@umsha.ac.ir.
authors.forename: Javad
authors.initials: J
authors.lastname: Faradmal
authors.forename: Atefeh
authors.initials: A
authors.lastname: Talebi
authors.forename: Abbas
authors.initials: A
authors.lastname: Rezaianzadeh
authors.forename: Hossein
authors.initials: H
authors.lastname: Mahjub
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000175:diagnosis / Q000401:mortality* / Q000473:pathology; D015331:Cohort Studies; D055088:Early Detection of Cancer / Q000401:mortality; D005260:Female; D006801:Humans; D007492:Iran / Q000453:epidemiology; D008198:Lymph Nodes / Q000473:pathology; D008207:Lymphatic Metastasis; D008875:Middle Aged; D011379:Prognosis; D016016:Proportional Hazards Models; D012307:Risk Factors; D016019:Survival Analysis; D055815:Young Adult