Like pretreatment prostate-specific antigen (PSA), post-treatment PSA
nadirs may have prognostic significance in patients with prostate
carcinoma, according to data presented by Timothy S. Boyd, MD, Robert
C. Orth, BS, Wolfgang A. Tomé, PhD, and Mark A. Ritter, MD,
PhD, of the Department of Human Oncology at the University of
Wisconsin at the American Society for Therapeutic Radiology and
Oncology (ASTRO) meeting.
Assuming that a stable PSA period occurring many years after
treatment equates with cure, the investigators focused on the extent
to which the probability of long-term cure decreased as the time
between treatment and the observed stable PSA interval decreased.
The Wisconsin researchers reviewed the PSA records of 296 patients
with prostate cancer initially treated with radiation therapy over a
9-year period. The final selection criteria for the study included
definitive treatment with irradiation, no post-treatment use of
antiandrogen therapy, and at least a 1-year period of stable PSA
values (defined two or more values below 1.0 or 0.5 ng/mL).
Any subsequent deviation from these criteria was defined as the onset
of biochemical failure. Clinical failures were defined by physical
examination and biopsy or imaging. From the time of completion of
each of the stable PSA periods, actuarial biochemical disease-free
survival was then calculated.
Patients with stable PSA periods below 1.0 ng/mL beginning 1 to 2
years after radiation therapy had a 5-year postinterval control rate
of 69%, increasing to 100% for stable PSA periods beginning 3 to 4
years after treatment. Patients with stable PSA periods below 0.5
ng/mL beginning 1 to 2 years after therapy had a 5-year postinterval
control rate of 92%, increasing to 100% for stable PSA periods
beginning 2 to 3 years after treatment. Patients in the nadir cohort
achieved a 5-year post nadir control rate of only 72% for nadirs £
1.0 ng/mL and a control rate of 73% for nadirs £
Therefore, the investigators concluded that PSA stability after
radiation is prognostically significant and may be useful as a study
end point and in counseling patients.