2553 - Clinical Outcomes of Patients with Oligometastatic Renal Cell Cancer Treated with Stereotactic Body Radiation Therapy: Results from a Prospective Registry Trial

K. N. Lee¹, Y. H. Chen², P. Doyle³, H. Kang⁴, M. Dillon-Martin⁵, T. Perkins⁶, D. E. Kozono⁷, B. McGregor⁸, W. Xu⁹, A. D. Choudhury¹⁰, T. A. Balboni⁷, A. Spektor¹¹, and M. A. Huynh¹¹; ¹Harvard Radiation Oncology Program, Boston, MA, ²Department of Data Science, Dana-Farber Cancer Institute, Boston, MA, ³Brigham and Womens Hospital/Dana-Farber, Boston, MA, United States, ⁴Boston University Chobanian & Avedisian School of Medicine, Boston, MA, ⁵Brigham and Womens Hospital/Dana-Farber, Boston, MA, ⁶Brigham and Womens Hospital, Boston, MA, ⁷Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, ⁸Dana Farber Cancer Institute, Boston, MA, ⁹Dana-Farber Cancer Institute, Boston, MA, ¹⁰Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, ¹¹Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA

Purpose/Objective(s): Metastatic renal cell carcinoma (RCC) has a poor prognosis and conventional radiotherapy has historically had limited utility given the radioresistant nature of RCC. With improving systemic therapies and improved technologies to deliver ablative doses, the role of stereotactic body radiation therapy (SBRT) in the treatment of oligometastatic RCC (oligoRCC) has gained interest and traction. Here, using a prospective cohort of oligoRCC patients treated with metastasis-directed SBRT, we investigate prognostic factors for clinical outcomes. Materials/

Methods: Using a single-institution registry trial, we analyzed a prospective cohort of 20 patients treated with metastasis-directed SBRT for oligoRCC from 2017 – 2024. Lesions were classified as synchronous, repeat, or induced oligometastatic disease (OMD) as per ESTRO-EORTC guidelines. Overall survival (OS) and time to next treatment (TTNT) was defined from time of SBRT start to time of death or date last known alive or initiation of next treatment, respectively. Lesions without disease radiographic progression or initiation of next treatment were censored at date of last follow-up. The Kaplan-Meier method, logrank test and Cox proportional hazards regression model were used to analyze time-to-event endpoints.
Results: Twenty patients with oligoRCC with 38 OMD lesions (range 1-6) were followed between 2017-2024, with median time from initial diagnosis to OMD of 11 months (range 0-192 months). The median age was 58.2 (range 38.1-82.2), with predominantly male patients (75%), clear cell histology (75%), and primary tumor controlled (75%, all with surgery), and with 1-3 OMD lesions (85%). 75% had more than one line of systemic therapy at time of SBRT. Most treated lesions were single sites of OMD (60%) with bone/spine metastases predominating (79%), and treated without concurrent systemic therapy (66%). SBRT fractionation included 20Gy/1F, 30Gy/3F, 30-60Gy/5F with 39% of treatments with . Median TTNT was 5.1 months (95% CI 3.7-11.3). Median OS was 40.4 months. Significantly, there was an association between OS and whether the primary site at the kidney was controlled (surgery) or had not received treatment (53.2 months vs 15.6 months, p=0.006). Similarly, OS was significantly associated with time from primary diagnosis to OMD diagnosis (<12 months: 23.7 months, 95% CI 11.8-40.4 vs =12 months: median OS not reached, 95% CI 53.2% - NR, p=0.002).
Conclusion: Using a prospective registry cohort of patients with oligoRCC treated with SBRT, we identify an association between OS and time of primary diagnosis to OMD = 12 months and control of the primary kidney site. These clinical factors can improve patient selection for oligoRCC SBRT. Further prospective studies are warranted.