Risk factors for PSA bounce following radiotherapy: outcomes from a multi-modal therapy analysis

To identify risk factors for PSA bounce (PSAb) and compare characteristics of prostate cancer patients treated with brachytherapy and external beam radiotherapy (EBRT).

We identified 362 patients treated for low risk prostate adenocarcinoma (D'Amico criteria) with a follow up time of at least 36 months. Patients received either: 1) EBRT 76 Gy in 38 fractions (n = 58); 2) hypofractionated EBRT, 45 Gy in 9 once-weekly fractions (n = 74); 3) seed brachytherapy (n = 230). PSAb was defined as a rise >= 0.2 ng/mL with subsequent return to baseline within the first 3 years after treatment. Univariate and multivariate logistic regression models were estimated to assess the association between clinical factors and occurrence of PSAb.

There was no significant difference between treatment groups (p = 0.349), with an overall PSAb rate of 28.5%. Upon univariate analysis, the following were predictive of a lower PSAb rate: older age (OR = 0.96), higher PSA at diagnosis (OR = 0.87), more positive biopsy cores (OR = 0.98), and a higher Cancer of the Prostate Risk Assessment (CAPRA) score (CAPRA of 3 versus 1: OR = 0.33). Multivariate analysis confirmed the significance of fewer positive biopsy cores (OR = 0.99) and a lower CAPRA score (CAPRA 3 versus 1: OR = 0.34). These factors also predicted a shorter time to first PSAb.

We found comparable rates of PSAb after different regimens of radiotherapy. We hypothesize that it results from late damage to healthy prostatic tissue. This idea is supported by the fact that we found that clinical factors indicative of a lower tumor burden were predictive of a PSAb.