Stereotactic Ablative Radiation Therapy for Oligoprogressive Renal Cell Carcinoma

Purpose: Oligoprogression, defined as limited sites of progression on systemic therapy, in patients with metastatic renal cell carcinoma (mRCC) is not uncommon, possibly because of inter- and intratumoral heterogeneity. We evaluated the effect of stereotactic ablative radiation therapy (SAbR) for longitudinal control of oligoprogressive mRCC. Methods and Materials: Patients with extracranial mRCC were included in this retrospective analysis if they progressed in ≤3 sites on systemic therapy while demonstrating response/stability at other sites and received SAbR to all progressing sites without switching systemic therapy. Our primary endpoint was modified progression-free survival (mPFS), which we calculated from the start of SAbR to the start of a subsequent systemic therapy, death, or loss to follow-up. Results: We identified 36 patients with a median follow-up of 20.4 months (interquartile range, 10.9-29.4). Forty-three sites were treated with SAbR with a median dose of 36 Gy (range, 18-50) in 3 fractions (range, 1-5). Median time to SAbR from the start of systemic therapy was 11.4 months (interquartile range, 6.1-17.1). Median mPFS was 9.2 months (95% confidence interval [CI], 5.9-13.2). Patients receiving SAbR while on immunotherapy exhibited a longer median mPFS (>28.4 months, log-rank P =.0001) than patients not on immunotherapy (9.2 months). Median overall survival from SAbR administration was 43.4 months (95% CI, 21.5-not Reached). The 1-year local control rate was 93% (95% CI, 78.7-97.5). Most SAbR-related toxicities were grade 1 to 2 (33% of patients), with one grade 5 hemoptysis event possibly related to SAbR or disease progression. Conclusions: SAbR has the potential to extend the the duration of current systemic therapy for selected patients with mRCC, preserving subsequent therapies for later administration possibly enabling longer treatment duration.