Stereotactic ablative body radiotherapy (SABR) is an option for oligometastatic clear cell renal cell carcinoma (ccRCC) but is limited by a lack of prospective clinical trial data.

The RAPPORT trial evaluated the safety and efficacy of total metastatic irradiation followed by short-course anti-programmed death receptor-1 immunotherapy in patients with oligometastatic ccRCC.

RAPPORT was a single-arm multi-institutional phase I/II trial (NCT02855203). Patients with two or fewer lines of prior systemic therapy and one to five oligometastases from ccRCC were eligible.

A single fraction of 20 Gy SABR (or if not feasible, ten fractions of 3 Gy) was given to all metastatic sites, followed by pembrolizumab 200 mg administered Q3W for eight cycles.

The endpoints were adverse events (AEs), disease control rate (DCR) for at least 6 mo, objective response rate (ORR), progression-free survival (PFS), and overall survival (OS). The Kaplan-Meier method was used for time-to-event endpoints. Freedom from local progression (FFLP) was assessed per lesion adding patient as a cluster effect.

Thirty evaluable patients, with a median age of 62 yr, were enrolled. The median follow-up was 28 mo. There were 44% of patients with intermediate-risk and 56% with favorable-risk disease. Eighty-three oligometastases were irradiated (median three per patient): eight adrenal, 11 bone, 43 lung, 12 lymph node, and nine soft tissue. Four patients (13%) had grade 3 treatment-related AEs: pneumonitis (n = 2), dyspnea (n = 1), and elevated alkaline phosphatase/alanine transaminase (n = 1). There were no grade 4 or 5 AEs. FFLP at 2 yr was 92%. ORR was 63% and DCR was 83%. Estimated 1- and 2-yr OS was 90% and 74%, respectively, and PFS was 60% and 45%, respectively. Limitations include a single-arm design and selected patient population.

SABR and short-course pembrolizumab in oligometastatic ccRCC is well tolerated, with excellent local control. Durable responses and encouraging PFS were observed, warranting further investigation.

The RAPPORT trial investigated the combination of high-dose precision radiotherapy and a short course of immunotherapy in patients with low-volume metastatic kidney cancer. We found that this treatment regimen was well tolerated, with excellent cancer control in sites of known disease. A proportion of patients were free from cancer relapse in the longer term, and these encouraging findings warrant further investigation.