Interim PSA: Predicting for biochemical failure during salvage radiotherapy following prostatectomy

Abstract Purpose; A subset of patients treated with post-prostatectomy radiotherapy for a biochemical recurrence after surgery fail to respond due to microscopic disease beyond the irradiated prostate bed. This work aims to determine if a rising interim PSA during radiotherapy can predict the likelihood of subsequent biochemical recurrence. Methods; Between the years of 2010 and 2016, 185 patients had salvage radiotherapy to a dose of 68 Gy without androgen deprivation therapy (ADT) for a rising prostate-specific antigen (PSA) level following radical prostatectomy. Patients had their PSA recorded on the first day of radiotherapy and again after completing the 25th fraction (of 34 total fractions). Biochemical failure after radiotherapy was defined as a PSA value ≥0.2ng/mL within two years following radiotherapy. Both univariate and multivariate Cox regression models were used for statistical analysis. Factors with a p value Results; The 2-year freedom from biochemical failure was 60% (95% CI: 53% to 67%). When assessing the interim PSA, 143 patients (77%) had a drop in interim PSA and of these patients, 71% had 2-year biochemical control. Forty-two patients (23%) had a stable or rising interim PSA, only 24% of these patients had 2-year biochemical control. On multivariate analysis, a drop in PSA during radiotherapy (p Conclusions; A PSA rise during salvage radiotherapy is prognostic of biochemical failure at two years. Factors such as seminal vesicle invasion and a negative surgical margin also predict for poor responders to salvage radiotherapy.