Predictive Factors for Oligometastatic Renal Cell Carcinoma Treated with Stereotactic Radiation: A Retrospective Study.

Abstract

Background and objective: Stereotactic ablative radiotherapy (SAbR) has shown promise in controlling oligometastatic renal cell carcinoma (omRCC). Careful patient selection is critical, and yet the selection criteria remain unknown for patients who will not be harmed by delayed systemic therapy using SAbR. Here, we analyzed long-term follow-up of omRCC patients treated with SAbR to derive the predictors of survival benefit.

Methods: We retrospectively reviewed patients with up to five omRCC sites treated with sequential SAbR from November 2007 to July 2022. Overall survival (OS), progression-free survival (PFS), local control (LC), and toxicity were analyzed. The predictors of PFS were analyzed using a univariate analysis and a Cox proportional hazard (CPH) model-based machine learning approach.

Key findings and limitations: We analyzed 153 patients who underwent SAbR to 337 metastases with a median follow-up of 27 mo. The median OS and PFS were 61.3 and 32 mo, respectively. The rate of grade ≥3 toxicity was 1.3%, and the 3-yr rate of LC was 98%. Patients with bone and brain metastases had lower PFS on the univariate analysis. When compared with historical controls, the delayed-onset PFS with first-line systemic therapy in this cohort was not compromised. The CPH model found bone, brain, and number of metastases at diagnosis to be the predictors of PFS, with a C-index of 0.66 and 1-yr area under the curve of 0.68.

Conclusions and clinical implications: For selected patients, SAbR is effective in controlling omRCC for >2 yr and can delay systemic therapy without compromising patient outcome. Bone and brain metastases, as well as an increasing number of metastases are poor predictive factors for omRCC patients treated with sequential SAbR who may benefit from upfront systemic therapy. Prospective studies are required to verify these findings.