Association of Nadir Prostate-specific Antigen > 0.5 ng/mL after Dose-escalated External Beam Radiation with Prostate Cancer-specific Endpoints

Objective Prior studies have suggested that prostate-specific antigen (PSA) nadir of 0.5 ng/mL is an important surrogate endpoint for prostate cancer-specific and all-cause mortality. This study analyzed our well-followed patient cohort to assess whether this endpoint was associated with differences in prostate cancer-specific endpoints in patients receiving dose-escalated radiation. Methods Patients with intermediate-or high-risk prostate cancer (>= T2b, or prostate-specific antigen > 10 ng/mL, or Gleason score >= 7) who were treated with external beam radiation to a minimum dose of 7560 cGy +/- androgen deprivation between 2003 and 2011 were identified. Biochemical control, distant metastasis-free survival (DMFS), prostate cancer-specific survival (PCSS), and overall survival (OS) were compared between those who achieved a nadir PSA <= 0.5 ng/mL with those who did not via Kaplan-Meier analysis. Univariable and multivariable Cox regression was performed on all endpoints to assess their impact on OS. Results There were 367 patients identified with a median follow-up of 99.5 months. Two hundred five patients (55.9%) received androgen deprivation for a median of 24 months (range 1-81 months). Most patients (n = 308, 83.9%) achieved a nadir PSA <= 0.5 ng/mL, which was associated with improvement across all endpoints at 10 years. This included biochemical control (68.0% versus 24.0%, p < 0.001), DMFS (89.6% versus 80.8%, p = 0.019), PCSS (91.1% versus 85.7%, p = 0.01), and OS (55.7% versus 45.8%, p = 0.048). On multivariable analysis, nadir PSA > 0.5 ng/mL remained strongly associated with worse outcomes across all endpoints. Conclusions Achievement of nadir PSA = 0.5 ng/mL after completion of dose-escalated radiation therapy was associated with improvement of all prostate cancer endpoints.