3491 - Factors Associated with Stereotactic Body Radiotherapy Use in Oligometastatic Uterine Cancer and Implications for Survival

C. Claunch¹, J. J. Thomas^1,2, A. Echeverria¹, M. S. Ludwig¹, C. Hoppenot³, T. R. Hall³, A. Costales², J. Sunde², A. S. Mohamed⁴, D. A. Hamstra¹, and S. Sharma¹; ¹Department of Radiation Oncology, Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, ²Baylor College of Medicine, Houston, TX, ³Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, ⁴Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s): Oligometastatic disease is an intermediate state between locoregional disease and widely metastatic disease. Previous work by our group showed a significant difference between the median survival of uterine cancer patients with a single metastatic site versus multiple sites, hence we defined our oligometastatic cohort as having one metastatic site at diagnosis. The aim of our current analysis was to explore the variables associated with stereotactic body radiotherapy (SBRT) use in this oligometastatic population and whether there are implications for survival. Materials/

Methods: The National Cancer Database was analyzed in patients diagnosed with uterine cancer between 2004-2019. We excluded patients with non-metastatic disease at diagnosis, lack of metastatic sites listed, multiple primaries, sarcoma and neuroendocrine histologies, and missing survival data. We included patients treated with radiotherapy and defined SBRT as =5 fractions and =500cGy dose per fraction. Univariable and multivariable logistic regression analyses were performed to assess the association of SBRT with covariates. Propensity score matching was then performed to match a cohort with patients treated with SBRT in a 1:3 ratio based on age, race/ethnicity, Charles-Deyo comorbidity index, grade, treatment and metastatic site. Survival analyses were performed using Kaplan-Meier analysis and log-rank tests.
Results: Among 641,276 women with uterine cancer, 13,974 remained after exclusion and 9,914 had oligometastatic disease with involvement of one metastatic site. In this population, 2,303 (23.2%) patients underwent radiotherapy and 70 (0.7%) were treated with SBRT. Univariable analysis identified the following variables to be significantly associated with SBRT: age, grade, housing, race/ethnicity, year of diagnosis and metastatic site. Upon multivariable analysis, the following variables remained significant: age (OR: 0.979; 95%CI: 0.956-1.00, p=8.62e-2); race: Black (OR: 0.271; 95%CI: 7.80e-2-0.712; p=1.77e-2); year of diagnosis (OR: 1.39; 95%CI: 1.22-1.60; p=1.76e-6); and metastatic site: bone (OR: 7.84 95%CI: 2.18-50.3; p=6.78e-3), brain (OR: 53.5; 95%CI: 14.8-345; p=1.85e-7). Survival analysis of oligometastatic patients treated and underwent propensity score matching showed a median overall survival of 24.6 months (95%CI: 16.5-NA) in the SBRT cohort versus 14.5 months (95%CI: 11.9-22) in the non-SBRT cohort (p=0.055).
Conclusion: SBRT use in oligometastatic uterine cancer was found to be increased in younger patients, metastatic sites involving bone or brain, and later years and was decreased in Black women. These results underscore potential missed opportunities for utilizing ablative techniques that may have implications for increasing overall survival in oligometastatic uterine cancer as suggested by our survival analysis.