A Biochemical Definition of Cure Following Brachytherapy for Prostate Cancer: A Multi-Institution International Study

14,496 patients with localized prostate cancer from 7 participating international institutions were treated with low-dose-rate (LDR) brachytherapy (BT), either alone as monotherapy (n=11,578), combined with androgen deprivation therapy (ADT) (n=1,965), combined with external beam radiotherapy (EBRT) (n=498), or combined with both ADT and EBRT (n=455). The objective was to determine whether a population can be defined that is cured based on long-term outcomes at 10 and 15 years after LDR BT using a surgical definition of biochemical failure, PSA≤0.2, as a biomarker. Analysis was based on PSA measured at 4 years (minimum follow-up of 3.5 years, range 3.5-4.5 years, n=9,011) post-treatment in patients who have not experienced clinical failure (CF). PSA measurements prior to the interval of interest were excluded, as were patients who failed clinically prior to the interval. Kaplan-Meier (KM) analysis was carried out using CF (local, distant, or regional) as endpoint for each of 4 PSA categories: PSA≤0.2 ng/ml, PSA >0.2 to ≤ 0.5 ng/ml, PSA > 0.5 to ≤ 1.0 ng/ml, and PSA>1.0 ng/ml. Results were validated through analysis of a prospective phase II trial of LDR BT alone for patients with intermediate-risk localized prostate cancer. The patients were distributed by risk category as 39% low-risk, 52% intermediate-risk, and 9% high-risk. The results of KM analysis are set out in the table below (95% CI in parentheses): The association of treatment success with PSA range was highly significant (p<0.0005). Over 2600 patients remained in follow-up beyond 10 years and >350 beyond 15 years; 93% maintained PSA≤0.2 10-15 years post-treatment. Analysis of the phase II study of LDR BT alone (all intermediate risk) showed that 99.4% of patients with a PSA≤0.2 were NED at 10 years post-treatment, with 95% CI (95.8%-99.9%). Patients with a PSA ≤ 0.2 ng/ml at 4 years post-treatment following LDR BT have >99% chance of remaining disease-free beyond 10 years. As this applies to more than 80% of patients in this study and has been validated in a prospective clinical trial cohort, we suggest that PSA ≤ 0.2 ng/ml be adopted as the biochemical definition of cure for LDR BT patients with ≥ 4 years follow-up.Abstract 115; Table 1PSA rangeNumber of patients in PSA range after 4 years%NED @ 10 y (238 CFs)%NED @ 15 y (195 CFs)PSA≤0.2740799.3(99.0-99.5)98.2(97.2-98.8)0.21.048761.0(54.6-66.8)50.1(40.7-58.8) Open table in a new tab