title: Modeling prostate specific antigen kinetics in patients on active surveillance.
abstract: OBJECTIVE
  Prostate specific antigen doubling time was used to stratify patients into groups at low and high risk for progression. The prostate specific antigen kinetics in these 2 groups were modeled.
  
  
  METHODS
  In this prospective, single-arm cohort study patients with favorable clinical parameters (stage T1b-T2b N0M0, Gleason score 7 or less, prostate specific antigen 15 ng/ml or less) were conservatively treated with watchful waiting. Evolution of serial prostate specific antigen measurements over time was estimated from a general linear mixed model of the natural log of prostate specific antigen. The corresponding average and individual prostate specific antigen doubling times were also calculated.
  
  
  RESULTS
  Since November 1995 a total of 231 patients had at least 6 months of followup and at least 3 prostate specific antigen measurements. Based on prostate specific antigen doubling time and repeat biopsy, 93 patients fulfilled the criteria for high risk of disease progression and 138 were defined as low risk. Given the baseline status of these individuals, 2 reference average lines (high risk and low risk) were derived to model the evolution of prostate specific antigen levels and permit more rational decision making regarding the need for definitive intervention. The average prostate specific antigen doubling time was 2.97 years (95% CI 2.2-4.4) in patients allocated to the high risk group and 6.54 years (95% CI 4.8-12.3) in those at low risk.
  
  
  CONCLUSIONS
  By applying the dynamic prognostic rule in combination with serial biopsy, a rational decision for definitive intervention based on the risk of disease progression could be optimally recommended about 2.3 years after initiated surveillance.
authors.affiliation: Division of Clinical Trials and Epidemiology, and Department of Radiation Oncology, and Division of Urology, Sunnybrook and Women's College Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Liying
authors.initials: L
authors.lastname: Zhang
authors.forename: Andrew
authors.initials: A
authors.lastname: Loblaw
authors.forename: Laurence
authors.initials: L
authors.lastname: Klotz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance; D011237:Predictive Value of Tests; D011446:Prospective Studies; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood* / Q000473:pathology*; D018570:Risk Assessment; D013997:Time Factors
chemical_list: D017430:Prostate-Specific Antigen