A zero PSA slope in posttreatment prostate-specific antigen supports cure of patients with long-term follow-up after external beam radiotherapy for localized prostate cancer

Abstract

Purpose To determine whether the rate of change in prostate-specific antigen (PSA) in patients treated with external beam radiotherapy for localized prostate cancer improves our ability to define which patients are likely to be cured of their disease. Methods and materials Patients treated between 1987 and 1995 at the University of California, San Francisco and the University of Michigan for localized prostate cancer with external beam radiotherapy and without hormonal ablation were evaluated for this study. The PSA slope was calculated for 199 patients who were disease free by the American Society for Therapeutic Radiology and Oncology consensus definition for at least 4 years and at last follow-up. Patients were categorized into groups defined by no increase, minimal increase, modest increase, and a definite increase in change in PSA level, corresponding to slopes of ≤0.0, >0.0–0.1, >0.1–0.5, and >0.5 ng/mL/y, respectively. Results Fifty-four percent of the patients displayed a non-increasing PSA (Group 1), 23% had a minimal increase (Group 2), 17% had a modest increase (Group 3), and 6% had a definite increase (Group 4). Patients with a non-increasing PSA slope had a significantly longer time to nadir (median 47.8, 31.6, 29.9, and 23.3 months for Groups 1–4, respectively, p = 0.0001) and a lower median PSA nadir (median 0.30, 0.40, 0.55, and 1.00 ng/mL for Groups 1–4, respectively, p = 0.0006). Conclusion On the basis of PSA kinetics, we believe that a group of patients can be defined who appear to be cured of localized prostate cancer (i.e., have a zero slope). These patients have a lower and later PSA nadir, as well as a more substantial proportional effect of external beam radiotherapy on their PSA level. Patients with a definite increase in PSA slope are erroneously labeled disease free by the American Society for Therapeutic Radiology and Oncology consensus definition.