S1241
Clinical - Urology
ESTRO 2026
using PSA, ISUP grade group, and T-stage, to create patient subgroups enriched with potentially pelvic- resistant characteristics. Kaplan-Meier estimates of disease-free survival (DFS) for these matched subgroups were analyzed to evaluate the added value of each trial intervention. We then performed a reverse analysis for FLAMEhigh-risk patients with recurrent disease despite receiving focal boost >80 Gy (FLAMErecc). Results: Of the 222 patients in the POP-RT trial, 15 had a recurrence despite receiving pelvic RT (POP-RTrecc ), while in the 344 high-risk patients from the FLAME trial (FLAMEhigh-risk), 22 had a clinical failure despite receiving tumour boost >80 Gy (FLAMErecc). Comparison of clinical characteristics between patients with recurrent disease and the corresponding full cohort (Figure 1) showed a significantly higher proportion of ISUP GG 4-5 (80% vs 49%, p= 0.040) in the POP-RTrecc subgroup, while the FLAMErecc group showed a higher proportion of patients with T3b+ disease (55% vs 33%, p=0.069).
In the POP-RTrecc matched population (Figure 2A), DFS was significantly improved by adding focal boost [HR 0.55 (0.31-0.98), p = 0.044] to standard prostate RT. In patients with clinical characteristics of FLAMErecc, Kaplan-Meier estimates were comparable for both matched arms of FLAMEhigh-risk and matched intervention arm of POP-RT (Figure 2B). However, within the matched POP-RT population addition of pelvic RT over prostate-only RT showed improved DFS [HR 0.47 (95% CI 0.23-0.98), p = 0.044].
Conclusion: In very high-risk prostate cancer, pelvic RT may improve DFS in stage ≥ cT3b disease regardless of a tumour boost, while ISUP grade group 4–5 patients may gain added benefit from a focal boost despite pelvic RT. References: [1] Murthy V. et al. Prostate-Only Versus Whole-Pelvic Radiation Therapy in High-Risk and Very High-Risk Prostate Cancer (POP-RT): Outcomes From Phase III Randomized Controlled Trial. J Clin Oncol. 2021.[2] Kerkmeijer L.G.W. et al. Focal Boost to the Intraprostatic Tumor in External Beam Radiotherapy for Patients With Localized Prostate Cancer: Results From the FLAME Randomized Phase III Trial. J Clin Oncol. 2021.[3] Menne Guricová K. et al. Focal Boost to the Intraprostatic Tumor in External Beam Radiotherapy for Patients With Localized Prostate Cancer: 10-Year Outcomes of the FLAME Trial. J Clin Oncol. 2025.[4] Ho D. et al. MatchIt: Nonparametric Preprocessing for Parametric Causal Inference. J. Stat. Softw. 2011. Keywords: pelvic irradiation, focal boosting, high-risk
Made with FlippingBook - Share PDF online