Delouya G et al. – Cox regression analysis for factors associated with biochemical failure. A total of 80/114 patterns were classified as having an exponential prostate–specific antigen (PSA) decline. Both exponential decline and PSA half life ratio were statistically significant predictors of biochemical failure. In the model predicting for exponential decline, none of the factors were significant. Patients with an exponential PSA decline show a better biochemical outcome in the long term.