3776 - Locoregional Radiotherapy Dose as a Prognostic Factor in Single Site Metastatic Endometrial Cancer
Presenter(s)
M. M. Flanagan1, C. Claunch2, A. N. Chavana3, J. Sunde3, D. A. Hamstra1, and S. Sharma1; 1Department of Radiation Oncology, Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, 2Department of Radiation Medicine, Oregon Health & Science University, Portland, OR, 3Baylor College of Medicine, Houston, TX
Purpose/Objective(s): Durable control may be achievable in oligometastatic endometrial cancer with aggressive multimodality therapy. We evaluated prognostic significance of locoregional radiotherapy (RT) in patients with solitary site synchronous metastatic uterine cancer (sSMUCa).
Materials/Methods: We performed a retrospective cohort study using the National Cancer Database (2004-2019), including women with epithelial uterine cancer and a single non-brain metastatic site at diagnosis who received multimodality therapy (MMT). Treatment strategies included systemic therapy plus surgery, trimodality (systemic + surgery + RT), or systemic therapy plus RT. Radiotherapy was stratified by field (locoregional vs metastasis-directed) and dose (=45 Gy vs <45 Gy). The dose threshold was selected based on observed dose distributions and conventional pelvic definitive dosing patterns. Overall survival (OS) was analyzed using Kaplan-Meier methods and multivariable Cox regression adjusting for age, tumor grade, comorbidity index, and race/ethnicity.
Results: Among 5,225 patients, median OS was 28.1 months. Trimodality therapy was associated with longer survival compared with systemic plus surgery alone (median OS 41.5 vs 27.7 months). Within trimodality therapy, locoregional (LR) RT =45 Gy was associated with the most favorable survival (median OS 62.0 months; adjusted HR 0.52; p<0.001), whereas LR RT <45 Gy was not associated with improvement (median OS 28.9 months; aHR 1.05; p=0.661). Only 8% of patients received LR RT =45 Gy within trimodality therapy. Among patients who did not undergo surgery, LR RT =45 Gy was associated with longer survival compared with LR RT <45 Gy (23.1 vs 11.0 months), though outcomes remained inferior relative to systemic plus surgery MMT.
Conclusion: In sSMUCa, locoregional radiotherapy =45 Gy dose independently stratified overall survival within multimodality treatment. Definitive dose pelvic radiotherapy was infrequently delivered, suggesting potential underutilization and supporting prospective evaluation within multidisciplinary management. .
*Multivariable model adjusted for age, tumor grade, Charlson-Deyo index, and race/ethnicity. Reference group: systemic therapy + LR surgery ± metastasis-directed surgery (no RT)| Treatment Modality | N | OS (mo) (95% CI) | Adjusted HR* (95% CI) | P value |
| Systemic + LR surgery (± met surgery) | 3591 | 27.7 (26.5-29.5) | Reference | — |
| Systemic + LR surgery (± met surgery) + LR RT =45 Gy | 422 | 62.0 (51.1-107.4) | 0.52 (0.44-0.61) | <0.001 |
| Systemic + LR surgery (± met surgery) + LR RT <45 Gy | 162 | 28.9 (24.1-38.5) | 1.05 (0.85-1.29) | 0.661 |
| Systemic + LR surgery (± met surgery) + met RT =45 Gy | 14 | 34.0 (20.8-57.7) | 0.85 (0.44-1.63) | 0.619 |
| Systemic + LR surgery (± met surgery) + met RT <45 Gy | 64 | 25.4 (19.1-36.2) | 1.17 (0.86-1.59) | 0.329 |
| Systemic + LR RT =45 Gy | 112 | 23.1 (18.4-33.3) | 1.33 (1.07-1.65) | 0.011 |
| Systemic + LR RT <45 Gy | 189 | 11.0 (9.7-12.4) | 2.31 (1.96-2.72) | <0.001 |