Alcántara P et al. (2006) Prostrate-specific antigen nadir within 12 months of prostrate cancer radiotherapy predicts metastasis and death. Cancer 28: 41–47

The nadir serum PSA level after radiotherapy is a good predictor of patient outcome; however, this value might not occur for several years. Alcántara and colleagues investigated whether the lowest PSA level in the 12 months that followed completion of radiotherapy (PSA levels fall >90% within this time) could predict patient outcome.

The authors enrolled 1,000 men with T1–3N0–xM0 prostate cancer, who had completed three-dimensional conformal radiotherapy (median dose 76 Gy) a minimum of 24 months before enrollment. Patients were then followed up every 6 months for 5 years, and every 6–12 months thereafter.

The lowest PSA level in the 12 months after radiotherapy independently predicted distant metastasis, overall mortality, prostate-cancer-specific mortality, and biochemical failure in the entire cohort. When a threshold 12-month PSA nadir value of 2 ng/ml was used, there were marked differences in the 10-year incidences of distant metastasis (19% versus 4%), biochemical failure (46% versus 30%), and prostate-cancer-specific mortality (7% versus 2%) for men with values above and below this threshold, respectively.

The authors note that the lowest PSA value in the 12 months following radiotherapy might be more clinically useful than PSA doubling time as a predictor of outcome, because PSA doubling time can only be calculated for a subset of patients. They conclude that the 12-month PSA nadir after radiotherapy could potentially identify patients at high risk of progression to biochemical failure, distant metastasis, and mortality, and has potential for use as a surrogate end point in clinical trials.