Use of PSA nadir to predict subsequent biochemical outcome following external beam radiation therapy for T1-2 adenocarcinoma of the prostate.
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.
Zietman
A L
AL
Department of Radiation, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Tibbs
M K
MK
Dallow
K C
KC
Smith
C T
CT
Althausen
A F
AF
Zlotecki
R A
RA
Shipley
W U
WU
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
D017430:Prostate-Specific Antigen