Proust-Lima C et al. (2008) Determinants of change in prostate-specific antigen over time and its association with recurrence after external beam radiation therapy for prostate cancer in five large cohorts. Int J Radiat Oncol Biol Phys 72: 782–791

Assessment of prostate-specific antigen (PSA) kinetics is often used to predict outcome after radiation therapy for localized prostate cancer. The decision to start salvage therapy is usually made before the development of symptomatic disease, and which PSA characteristics should be used for treatment decisions remains unclear. Proust-Lima and colleagues have developed an approach based on the relationships between prognostic factors, postradiotherapy PSA kinetics and clinical recurrence to provide an accurate picture of the risk of recurrence.

The authors analyzed 40,324 PSA measurements from 4,247 patients treated with radiation therapy. A linear mixed model was used to describe the pattern of PSA changes after radiotherapy. A Cox model was then used to determine the association between prognostic factors, post-treatment PSA behavior and time to recurrence.

Clinical recurrences were observed in 12.2% of the patients. Short-term declines in PSA levels after radiation were significantly associated with pretreatment PSA and tumor stage. High values of pretreatment PSA, tumor-stage and Gleason score were associated with steep subsequent increases in PSA. A high current PSA level and steep rate of PSA increase were both associated with a high risk of recurrence.

The authors conclude that a joint linear mixed model can be used to assess the PSA kinetics and risk of recurrence after radiation therapy for prostate cancer and have developed a risk calculator for others to use.