3374 - Impact of Short-Term ADT on Survival in Unfavorable Intermediate-Risk Prostate Cancer Treated with Proton-Beam Radiotherapy - A Retrospective Cohort Study
Presenter(s)
K. Shin1, M. K. Rooney1, C. Tang1, H. Mok1, C. J. Hassanzadeh1, Q. N. Nguyen1, S. E. McGuire1, K. E. Hoffman1, S. J. Frank2, P. T. Tran1, and S. Choi1; 1Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 2Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s): Short-term androgen deprivation therapy (ADT) is standard in combination with external beam radiotherapy for unfavorable intermediate risk prostate cancer (UI-PCa). Given the dosimetric advantages of proton beam therapy (PBT), the incremental survival benefit of short-term ADT in patients treated with definitive PBT remains uncertain. We compared survival outcomes in patients with unfavorable intermediate risk prostate cancer treated with definitive PBT with or without short term ADT.
Materials/Methods: Patients diagnosed with UI-PCa and received definitive PBT with or without =6 months of ADT between May 2006 and Jan 2020 were identified from institutional database retrospectively. The primary outcome was biochemical recurrence-free survival (bRFS), defined by phoenix criteria (PSA = nadir+2 ng/mL). Secondary outcomes were overall survival (OS) and distant metastasis-free survival (DMFS), where progression was defined as biochemical and/or radiographic progression. Kaplan-Meier method and log-rank test were used for survival estimation and propensity score matching was performed to limit confounding effects. Cox proportional hazards model with interaction term was used to evaluate adjusted effects.
Results: Of 470 patients, 366 (77.9%) patients received ADT (median follow-up: 78 mo). These patients showed higher proportion of T2b/T2c stage, Gleason 7(4+3), >50% positive cores, but lower PSA at diagnosis. At 5 years, ADT was associated with higher bRFS, which was not statistically significant (98.9% vs 96.6%, p=0.2). By 8 years, this difference reversed (93.2% vs 95.2%). ADT did not improve OS (5yr: 93.8% vs 96.9%, 8yr: 89.1% vs 94.4%, p=0.9). ADT was not related to statistically significant benefits in DMFS (5yr: 98.7% vs 99.0%, 8yr: 98.0% vs 97.7%, p=0.4). In a matched cohort, the same trend was observed, but none of the differences were statistically significant ([bRFS] 5yr: 100% vs 96.5%, 8yr: 90.3% vs 95.1%, p=0.4; [OS] 5yr: 95.4% vs 96.8%, 8yr: 93.3% vs 94.2%, p=0.5; [DMFS] 5yr: 97.5% vs 99.0%, 8yr: 97.5% vs 97.6%, p=0.8). No statistically significant interaction was shown between ADT status and T stage, Gleason group, baseline PSA, and percentage of positive cores.
Conclusion: In this retrospective cohort, the addition of short-term ADT to PBT for unfavorable intermediate-risk prostate cancer was not associated with a sustained improvement in biochemical control or survivals. These findings suggest that the incremental benefit of short-term ADT with PBT may be smaller than historically observed with photon therapy and warrant prospective validation.