title: Use of PSA nadir to predict subsequent biochemical outcome following external beam radiation therapy for T1-2 adenocarcinoma of the prostate.
abstract: OBJECTIVE
  This study assessed the ability of nadir prostate-specific antigen (PSA) to act as an early surrogate for subsequent freedom from biochemical failure following radiation therapy for T1-2 prostatic adenocarcinoma.
  
  
  METHODS
  A retrospective analysis was performed on the biochemical outcome of 314 consecutive men with T1-2 disease treated by conventional external beam radiation at the Massachusetts General Hospital. Minimum follow up was 2 years, and failure was defined as three successive rises in serum PSA of greater than 10%. Kaplan-Meier actuarial analysis of outcome was employed.
  
  
  RESULTS
  The overall 5-year freedom from biochemical progression was 63%. For those who achieved a PSA nadir of < or = 0.5 ng/ml (n = 123) it was 90%, for 0.6-1.0 ng/ml (n = 103) it was 55%, and for > 1.0 ng/ml (n = 88) it was 34%. Multivariate analysis showed an undetectable PSA nadir to be independent of Gleason grade and initial PSA in predicting subsequent outcome (P < 0.05). The likelihood of achieving an undetectable PSA nadir correlated strongly with the pretreatment value: 74% if this was below 4 ng/ml; 42% for those between 4.1 and 10 ng/ml; and 32% for those above 10 ng/ml.
  
  
  CONCLUSIONS
  A PSA nadir of < or = 0.5 ng/ml represents an early endpoint strongly predictive of a favorable outcome following radiation therapy which may be used for the rapid assessment of new radiation strategies.
authors.affiliation: Department of Radiation, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Zietman
authors.forename: M K
authors.initials: MK
authors.lastname: Tibbs
authors.forename: K C
authors.initials: KC
authors.lastname: Dallow
authors.forename: C T
authors.initials: CT
authors.lastname: Smith
authors.forename: A F
authors.initials: AF
authors.lastname: Althausen
authors.forename: R A
authors.initials: RA
authors.lastname: Zlotecki
authors.forename: W U
authors.initials: WU
authors.lastname: Shipley
mesh_terms: D000206:Actuarial Analysis; D000230:Adenocarcinoma / Q000097:blood / Q000473:pathology / Q000532:radiotherapy*; D016022:Case-Control Studies; D018450:Disease Progression; D006801:Humans; D008297:Male; D015999:Multivariate Analysis; D009367:Neoplasm Staging; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood / Q000473:pathology / Q000532:radiotherapy*; D012189:Retrospective Studies; D017211:Treatment Failure
chemical_list: D017430:Prostate-Specific Antigen