J Clin Oncol. 2024 Mar 12:JCO2300762. Online ahead of print.

Lucia Kwak, Praful Ravi, John G Armstrong, Veronique Beckendorf, Joseph L Chin, Anthony V D'Amico, David P Dearnaley, Savino M Di Stasi, Silke Gillessen, Himanshu Lukka, Nicolas Mottet, Pascal Pommier, Wendy Seiferheld, Matthew R Sydes, Bertrand Tombal, Almudena Zapatero, Meredith M Regan, Wanling Xie, Christopher J Sweeney

Purpose: We sought to evaluate the prognostic impact of prostate-specific antigen (PSA) at 6 months after completion of radiotherapy (RT) in patients treated with RT alone, RT plus short-term (st; 3-6 months), and RT plus long-term (lt; 24-36 months) androgen-deprivation therapy (ADT).

Patients and methods: Individual patient data were obtained from 16 randomized trials evaluating RT ± ADT for localized prostate cancer (PCa) between 1987 and 2011. The lowest PSA recorded within 6 months after RT completion was identified and categorized as < or ≥0.1 ng/mL. The primary outcomes were metastasis-free survival (MFS), PCa-specific mortality (PCSM), and overall survival (OS), from 12 months after random assignment.

Results: Ninety-eight percent (n = 2,339/2,376) of patients allocated to RT alone, 84% (n = 4,756/5,658) allocated to RT + stADT, and 77% (n = 1,258/1,626) allocated to RT + ltADT had PSA ≥0.1 ng/mL within 6 months after completing RT. PSA ≥0.1 ng/mL was associated with lower MFS and OS and higher PCSM among patients allocated to RT ± ADT (RT - MFS: hazard ratio [HR], 2.24 [95% CI, 1.21 to 4.16]; PCSM: subdistribution hazard ratio [sHR], 1.82 [0.51 to 6.49]; OS: HR, 1.72 [0.97 to 3.05]; RT + stADT - MFS: HR, 1.27 [1.12 to 1.44]; PCSM: sHR, 2.10 [1.52 to 2.92]; OS: HR, 1.26 [1.11 to 1.44]; RT + ltADT - MFS: HR, 1.58 [1.27 to 1.96]; PCSM: sHR, 1.97 [1.11 to 3.49]; OS: HR, 1.59 [1.27 to 1.99]). Five-year MFS rates among patients allocated to RT, RT + stADT, and RT + ltADT were 91% versus 79%, 83% versus 76%, and 87% versus 74%, respectively, based on PSA < or ≥0.1 ng/mL.

Conclusion: PSA ≥0.1 ng/mL within 6 months after RT completion was prognostic for lt outcomes in patients treated with RT ± ADT for localized PCa. This can be used to counsel patients treated with RT ± ADT and in guiding clinical trial design evaluating novel systemic therapies with RT + ADT as well as (de)intensification strategies.