title: Identifying the most appropriate age threshold for TNM stage grouping of well-differentiated thyroid cancer.
abstract: OBJECTIVE
  Age is integrated in most risk stratification systems for well-differentiated thyroid cancer (WDTC). The most appropriate age threshold for stage grouping of WDTC is debatable. The objective of this study was to evaluate the best age threshold for stage grouping by comparing multivariable models designed to evaluate the independent impact of various prognostic factors, including age based stage grouping, on the disease specific survival (DSS) of our population-based cohort.
  
  
  METHODS
  Data from population-based thyroid cancer cohort of 2125 consecutive WDTC, diagnosed during 1970-2010, with a median follow-up of 11.5 years, was used to calculate DSS using the Kaplan Meier method. Multivariable analysis with Cox proportional hazard model was used to assess independent impact of different prognostic factors on DSS. The Akaike information criterion (AIC), a measure of statistical model fit, was used to identify the most appropriate age threshold model. Delta AIC, Akaike weight, and evidence ratios were calculated to compare the relative strength of different models.
  
  
  RESULTS
  The mean age of the patients was 47.3 years. DSS of the cohort was 95.6% and 92.8% at 10 and 20 years respectively. A threshold of 55 years, with the lowest AIC, was identified as the best model. Akaike weight indicated an 85% chance that this age threshold is the best among the compared models, and is 16.8 times more likely to be the best model as compared to a threshold of 45 years.
  
  
  CONCLUSIONS
  The age threshold of 55 years was found to be the best for TNM stage grouping.
authors.affiliation: Section of Surgical Oncology, CancerCare Manitoba, Department of Surgery, University of Manitoba, Winnipeg R3E 0V9, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Hendrickson-Rebizant
authors.affiliation: Section of Surgical Oncology, CancerCare Manitoba, Department of Surgery, University of Manitoba, Winnipeg R3E 0V9, Canada.
authors.forename: H
authors.initials: H
authors.lastname: Sigvaldason
authors.affiliation: Section of Surgical Oncology, CancerCare Manitoba, Department of Surgery, University of Manitoba, Winnipeg R3E 0V9, Canada.
authors.forename: R W
authors.initials: RW
authors.lastname: Nason
authors.affiliation: Section of Surgical Oncology, CancerCare Manitoba, Department of Surgery, University of Manitoba, Winnipeg R3E 0V9, Canada. Electronic address: alok.pathak@cancercare.mb.ca.
authors.forename: K A
authors.initials: KA
authors.lastname: Pathak
mesh_terms: D017668:Age of Onset; D000368:Aged; D005260:Female; D005544:Forecasting; D006801:Humans; D015994:Incidence; D008297:Male; D008350:Manitoba / Q000453:epidemiology; D008875:Middle Aged; D009367:Neoplasm Staging / Q000379:methods*; D011379:Prognosis; D012189:Retrospective Studies; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D015996:Survival Rate / Q000639:trends; D013964:Thyroid Neoplasms / Q000453:epidemiology* / Q000473:pathology*
keywords: Outcome; Prognosis; Risk stratification; Staging; Survival; Thyroid carcinoma