Purpose: A method that allows the determination of a prostate-specific antigen (PSA) cure after definitive management for prostate carcinoma with radiation therapy is presented and tested.
Methods and materials: The method involves a calculation of the patient's theoretical baseline PSA prior to the development of prostate cancer by using three serial rising PSA determinations obtained prior to the institution of therapy. The rate of rise of the PSA prior to therapy and the rate of decline of the PSA posttherapy are calculated, using an exponential model. Two criteria must be satisfied to define a PSA cure. First, the PSA nadir after treatment should be less than the calculated theoretical baseline PSA. Second, the rate of decline of PSA posttreatment should be greater than the rate of rise of the PSA prior to treatment.
Results: Applying these two criteria to the patient data base (n = 16) at a median follow-up of 19 months enabled the accurate prediction of 6 out of 6 (100%) of patients with documented PSA failure and 7 out of 10 (70%) of patients without PSA failure. Therefore, despite short follow-up, all six patients with PSA failure were predicted. Further follow-up is needed to ascertain if the seven patients predicted to be cured will remain PSA failure free and if the three patients currently without PSA failure in whom the model predicts failure, will subsequently fail.
Conclusion: Therefore, using each patient's PSA history as the natural control may eliminate the error that is introduced with defining a PSA cure by using a single value for the PSA nadir at a specified time after radiation therapy.