Detectable prostate-specific antigen after radiotherapy for clinically localized prostate cancer.

[BACKGROUND] This study assesses the incidence and timing of undetectable prostate-specific antigen (PSA) after radiotherapy (RT) ± androgen deprivation therapy (ADT) and its association with prostate cancer mortality.

[METHODS] This is a population-based study including 5299 men undergoing RT (2006-2020) in the Stockholm County, Sweden with all their PSA tests until death or emigration. The authors calculated incidence and timing of undetectable PSA (PSA ≤0.1 ng/mL) and used competing risk regression to evaluate the association of detectable PSA at 6 and 12 months with prostate cancer mortality (PCSM).

[RESULTS] Median follow-up for survivors was 81 (32, 130) months. PSA nadir values were reached before 6 and 12 months in 233 (23%) and 470 (36%) patients undergoing RT and 2871 (85%) and 3612 (90%) patients undergoing RT+ADT. No significant association was found between PSA at nadir, 6 and 12 months and PCSM in the radiotherapy group and evidence of association with higher PCSM in RT+ADT group (PSA at nadir: subdistribution hazard ratio [sHR], 2.23 [2.01-2.49]; PSA at 6 months: sHR, 6.91 [5.17-9.23]; and PSA at 12 months: sHR, 37.9 [23.0-62.5]). At 12 years after RT + ADT, PCSM rates were 27%, 15%, 13%, and 5% for patients with PSA at 6 months of ≥0.5, 0.2-0.5, 0.1-0.2, and ≤0.1 ng/mL, respectively; corresponding rates by PSA at 12 months were 34%, 18%, 12%, and 5%.

[CONCLUSIONS] Most patients undergoing RT+ADT reached a PSA ≤0.1 ng/mL within 6 and 12 months. PSA>0.1 ng/mL at these time points indicated a higher risk of PCSM, emphasizing the need for timely restaging and intensified salvage treatments.