3255 - 4-Year PSA Response and Long-Term Cancer Outcomes in Men Treated with Definitive External Beam Radiotherapy (EBRT) and High Dose Rate Brachytherapy Boost (HDRBT)

12:45pm - 02:00pm PT

Hall F

Screen: 15

POSTER

Presenter(s)

Therese Kang, MBBS - Alfred Health, Melbourne, VIC

T. Kang^1,2, J. Bensley³, J. L. Millar^1,2, and W. L. Ong^1,2; ¹School of Translational Medicine, Monash University, Melbourne, Australia, ²Alfred Health Radiation Oncology, Melbourne, VIC, Australia, ³Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Melbourne, VIC, Australia

Purpose/Objective(s): Multiple studies have shown that PSA response at 4 years (4yrPSA) is predictive of long-term cancer outcomes in men with prostate cancer treated with low dose rate brachytherapy and stereotactic ablative body radiotherapy. The aim of this study was to investigate 4yrPSA on long-term cancer outcomes in men treated with EBRT+HDRBT.

Materials/Methods: This was a single institutional retrospective study of men with NCCN intermediate risk (IRPC) to high risk (HRPC) prostate cancer who had EBRT+HDRBT, between 1998 and 2024. Men with IRPC and HRPC had 6 months and 30 months ADT respectively. The 4yrPSA was dichotomized based on PSA <0.4 ng/mL or PSA ³0.4 ng/mL. Cox regression and Fine-Gray models were used to test whether 4yrPSA was associated with biochemical recurrence (BCR), distant metastases free survival (DMFS), prostate cancer specific mortality (PCSM), and overall survival (OS). Multivariable analyses were performed to evaluate association of 4yrPSA with BCR, DMFS, PCSS, and OS, adjusting for ISUP Grade Group, PSA at diagnosis, clinical T categories, and duration of ADT.

Results: There were 412 men included in this analysis, of which 200 (48.66%) had IRPC and 211 (51.34%) had HRPC. The median follow-up for the cohort was 14.8 years (IQR: 10.33-18.67 years). The median PSA at 4 year was 0.1 ng/mL (IQR: 0.06-0.2). There were 348 (84.47%) and 64 (15.53%) men who had 4yrPSA <0.4 ng/mL and 4yrPSA ³0.4 ng/mL respectively. The 10-year cumulative incidence of BCR was 17.24% (95%CI=8.45-28.63%) for patients with 4yrPSA <0.4 ng/mL and 88.81% (95%CI=84.75-91.84%) for patients with 4yrPSA ³0.4 ng/mL (P<0.0001). The 10-year DMFS was 97.76% (95%CI=95.34-98.93%) for patients with 4yrPSA <0.4 ng/mL and 85.69% (95%CI=73.32-92.60%) for patients with 4yrPSA ³0.4 ng/mL (P<0.0001). The 10-year cumulative incidence of PCSM was 10.22% (95%CI=7.37-14.08%) for patients with 4yrPSA <0.4 ng/mL and 39.76% (95%CI=28.87-52.95%) for patients with 4yrPSA ³0.4 ng/mL (P<0.0001). The 10-year OS was 89.78% (95%CI=85.92-92.63%) for patients with 4yrPSA <0.4 ng/mL and 60.24% (95%CI=47.05-71.13%) for patients with 4yrPSA ³0.4 ng/mL (P<0.0001). In multivariable analyses, after adjusting for pre-defined covariables, 4yrPSA <0.4 ng/mL was associated with improved BCR (HR = 0.08; 95%CI = 0.05-0.12; P<0.0001) and DMFS (HR = 0.18; 95%CI = 0.11-0.33, P<0.0001), reduced PCSM (HR = 0.09; 95%CI = 0.05-0.16; P<0.0001), and improved OS (HR = 0.33; 95%CI = 0.23-0.46, P<0.0001).

Conclusion: In this single-institutional cohort of men with IRPC and HRPC, we confirmed that 4yrPSA is an early predictor of long-term cancer outcomes following treatment with EBRT and HDRBT.