Prostate-specific Antigen Bounce After Stereotactic Body Radiotherapy for Prostate Cancer: A Pooled Analysis of Four Prospective Trials

• Published in: Clinical oncology (Royal College of Radiologists (Great Britain)) Vol. 31; no. 9; pp. 621 - 629
• Main Authors: Roy, S., Loblaw, A., Cheung, P., Chu, W., Chung, H.T., Vesprini, D., Ong, A., Chowdhury, A., Panjwani, D., Pang, G., Korol, R., Davidson, M., Ravi, A., McCurdy, B., Helou, J., Zhang, L., Mamedov, A., Deabreu, A., Quon, H.C.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-09-2019
• Subjects: Aged; Follow-Up Studies; Humans; Male; Middle Aged; Prospective Studies; Prostate cancer; Prostate-Specific Antigen - metabolism; Prostatic Neoplasms - radiotherapy; PSA bounce; Radiosurgery - methods; stereotactic body radiotherapy; time–dose fractionation; stereotactic body radiotherapy; Prostate cancer; time–dose fractionation; PSA bounce
• ISSN: 0936-6555; 1433-2981
• DOI: 10.1016/j.clon.2019.05.001

We conducted a pooled analysis of four prospective stereotactic body radiotherapy (SBRT) trials of low- and intermediate-risk prostate cancer to evaluate the incidence of prostate-specific antigen (PSA) bounce and its correlation with the time–dose–fraction schedule. The correlation between bounce with PSA response at 4 years (nadir PSA < 0.4 ng/ml) and biochemical failure-free survival (BFFS) was also explored.
The study included four treatment groups: 35 Gy/five fractions once per week (QW) (TG-1; n = 84); 40 Gy/five fractions QW (TG-2; n = 100); 40 Gy/five fractions every other day (TG-3; n = 73); and 26 Gy/two fractions QW (TG-4; n = 30). PSA bounce was defined as a rise in PSA by 0.2 ng/ml (nadir + 0.2) or 2 ng/ml (nadir + 2.0) above nadir followed by a decrease back to nadir. Patients with fewer than three follow-up PSA tests were excluded from the pooled analysis.
In total, 287 patients were included, with a median follow-up of 5.0 years. The pooled 5-year cumulative incidence of bounce by nadir + 2.0 was 8%. The 2-year cumulative incidences of PSA bounce by nadir + 0.2 were 28.9, 21, 19.6 and 16.7% (P = 0.12) and by nadir + 2.0 were 7.2, 8, 2.7 and 6.7% (P = 0.32) for TG-1 to TG-4, respectively. Multivariable analysis revealed that for nadir + 2.0, pre-treatment PSA (odds ratio 0.49; 95% confidence interval 0.26–0.97) correlated with PSA bounce. Although PSA bounce by nadir + 0.2 (odds ratio 0.10; 95% confidence interval 0.04–0.24) and nadir + 2.0 (odds ratio 0.29; 95% confidence interval 0.09–0.93) was associated with a lower probability of PSA response at 4 years, there was no association between bounce by nadir + 0.2 (hazard ratio 0.36; 95% confidence interval 0.08–1.74) or nadir + 2 (hazard ratio 1.77; 95% confidence interval 0.28–11.07) with BFFS.
The incidence of PSA bounce was independent of time–dose–fraction schedule for prostate SBRT. One in 13 patients experienced a bounce high enough to be misinterpreted as biochemical failure, and clinicians should avoid early salvage interventions in these patients. There was no association between PSA bounce and BFFS.
•No correlation between PSA bounce probability and dose-fraction schedules of SBRT.•One in 13 patients has a bounce high enough to be misdiagnosed as biochemical failure.•PSA bounce was not associated with biochemical failure-free survival.