title: Cox models survival analysis based on breast cancer treatments.
abstract: BACKGROUND
  The aim of this study is to evaluate the association between different treatments and survival time of breast cancer patients using either standard Cox model or stratified Cox model.
  
  
  METHODS
  The study was conducted on 15830 women diagnosed with breast cancer in British Columbia, Canada. They were divided into eight groups according to patients' ages and stage of disease Either Cox's PH model or stratified Cox model was fitted to each group according to the PH assumption and tested using Schoenfeld residuals.
  
  
  RESULTS
  The data show that in the group of patients under age 50 years old and over age 50 with stage I cancer, the highest hazard was related to radiotherapy (HR= 3.15, CI: 1.85-5.35) and chemotherapy (HR= 3, CI: 2.29- 3.93) respectively. For both groups of patients with stage II cancer, the highest risk was related to radiotherapy (HR=3.02, CI: 2.26-4.03) (HR=2.16, CI:1.85-2.52). For both groups of patients with stage III cancer, the highest risk was for surgery (HR=0.49, CI: 0.33-0.73), (HR=0.45, CI: 0.36-0.57). For patients of age 50 years or less with stage IV cancer, none of the treatments were statistically significant. In group of patients over age 50 years old with stage IV cancer, the highest hazard was related to surgery (HR=0.64, CI: 0.53-0.78).
  
  
  CONCLUSIONS
  The results of this study show that for patients with stage I and II breast cancer, radiotherapy and chemotherapy had the highest hazard; for patients with stage III and IV breast cancer, the highest hazard was associated with treatment surgery.
authors.affiliation: Dept. of Health and Community Medicine, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Alireza
authors.initials: A
authors.lastname: Abadi
authors.affiliation: Dept. of Health and Community Medicine, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Parvin
authors.initials: P
authors.lastname: Yavari
authors.affiliation: Dept. of Biostatistics, Paramedical Sciences Faculty, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Monireh
authors.initials: M
authors.lastname: Dehghani-Arani
authors.affiliation: Dept. of Biostatistics, Paramedical Sciences Faculty, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Hamid
authors.initials: H
authors.lastname: Alavi-Majd
authors.affiliation: Dept. of Biostatistics, Paramedical Sciences Faculty, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Erfan
authors.initials: E
authors.lastname: Ghasemi
authors.affiliation: Dept. of Biostatistics, Paramedical Sciences Faculty, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Farzaneh
authors.initials: F
authors.lastname: Amanpour
authors.affiliation: Cancer Control Research Program, BC Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Chris
authors.initials: C
authors.lastname: Bajdik
keywords: Breast cancer; Cox PH regression; Stratified Cox model; Treatment