title: Prognostic Factors as a Function of Disease-free Interval After Definitive (Chemo)radiation for Non-Small Cell Lung Cancer Using Conditional Survival Analysis.
abstract: OBJECTIVE
  We analyzed overall and disease-free survival (OS and DFS) after definitive (chemo)radiation for stage III non-small cell lung cancer with 2 statistical methods: Kaplan-Meier (KM) analysis, with diagnosis as index date, and conditional survival (CS) analysis, with a variety of disease-free index dates, and determined whether prognostic factors varied based on the reference date.
  
  
  METHODS
  All 651 patients analyzed received definitive (chemo)radiotherapy for stage III non-small cell lung cancer in November 1998 to December 2010 at a single institution; all had Karnofsky performance status scores ≥60 and received ≥60 Gy. OS and DFS were first calculated with the KM method, and then CS was used to calculate 2 outcomes: OS conditioned on DFS time (OS|DFS) and DFS conditioned on DFS time (DFS|DFS). Factors predicting OS and DFS conditioned on 1-, 2-, and 3-year DFS were sought in univariate and multivariate analyses.
  
  
  RESULTS
  KM analysis produced 1-, 2-, and 3-year DFS rates of 48%, 30%, and 26%; OS rates were 64%, 41%, and 29%. By CS analysis, both OS|DFS and DFS|DFS showed an increase in 5-year OS after 6 months, and CS after 30 months approached 100%. On multivariate analyses, age and concurrent chemoradiation predicted OS|DFS; age, smoking history, tumor histology, disease stage, and radiation dose predicted DFS|DFS.
  
  
  CONCLUSIONS
  CS analysis showed that the probability of long-term survival increases sharply after 6 months with no evidence of disease; factors predicting survival differed based on the method and endpoint used.
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Jidong
authors.initials: J
authors.lastname: Hong
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhuang
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Lawrence B
authors.initials: LB
authors.lastname: Levy
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Tommy
authors.initials: T
authors.lastname: Sheu
authors.affiliation: Thoracic/Head & Neck Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX.
authors.forename: John V
authors.initials: JV
authors.lastname: Heymach
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Quynh-Nhu
authors.initials: QN
authors.lastname: Nguyen
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Ting
authors.initials: T
authors.lastname: Xu
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
authors.affiliation: Departments of Radiation Oncology.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Gomez
mesh_terms: D000328:Adult; D000368:Aged; D002289:Carcinoma, Non-Small-Cell Lung / Q000401:mortality* / Q000473:pathology / Q000628:therapy*; D002423:Cause of Death; D059248:Chemoradiotherapy / Q000379:methods* / Q000401:mortality; D015331:Cohort Studies; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D017567:Karnofsky Performance Status; D008175:Lung Neoplasms / Q000401:mortality* / Q000473:pathology / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009361:Neoplasm Invasiveness / Q000473:pathology; D009367:Neoplasm Staging; D011237:Predictive Value of Tests; D011379:Prognosis; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D016019:Survival Analysis