Editor’s Note: At a recent international academic symposium, Dr. Aly-Khan A. Lalani from McMaster University presented the primary results of the CYTOSHRiNk study (Abstract 416). This randomized Phase II trial evaluated the efficacy and safety of cytoreductive stereotactic body radiotherapy (SBRT) combined with nivolumab plus ipilimumab (Nivo+Ipi) in patients with treatment-naïve metastatic clear cell renal cell carcinoma (mRCC).01 Background: Shifting from Surgical Cytoreduction to Non-invasive Radiotherapy
Approximately one-third of renal cell carcinoma (RCC) patients present with de novo metastatic disease. While nivolumab plus ipilimumab has become the standard first-line treatment for IMDC intermediate- and poor-risk mRCC, the presence of the primary kidney mass may limit the overall benefit of systemic therapy.
Findings from the CARMENA and SURTIME trials challenged the routine use of upfront cytoreductive nephrectomy (CN) in the targeted therapy era. SBRT, as a non-invasive, precise technique with potential immunomodulatory effects, offers a novel alternative to CN. Dr. Lalani’s team hypothesized that SBRT directed at the primary renal mass could not only achieve cytoreduction but also enhance the efficacy of Nivo+Ipi through immune synergy.
02 Study Design: The CYTOSHRiNk Randomized Framework
The CYTOSHRiNk trial enrolled treatment-naïve IMDC intermediate- or poor-risk mRCC patients with a primary kidney lesion amenable to SBRT (up to 20 cm).
- Randomization: Patients were randomized 2:1.
- Experimental Arm (SBRT + Nivo + Ipi): Received Cycle 1 of Nivo+Ipi, followed by SBRT to the primary lesion (30–40 Gy in 5 fractions), then Cycles 2–4 of Nivo+Ipi, and subsequent nivolumab maintenance.
- Control Arm (Standard Nivo + Ipi): Received the standard four cycles of Nivo+Ipi followed by nivolumab maintenance.
- Endpoints: The primary endpoint was the 1-year progression-free survival (PFS) rate. Secondary endpoints included safety, objective response rate (ORR), overall survival (OS), and health-related quality of life.
03 Baseline Characteristics: Imbalances in Disease Burden
A total of 67 patients were randomized (43 in the experimental arm, 24 in the control arm). Notably, despite randomization, several baseline imbalances were observed:
- Tumor Burden: Patients in the experimental arm had larger primary renal masses and a higher frequency of T3/T4 stage lesions.
- Metastatic Sites: The experimental arm had a significantly higher prevalence of poor-prognostic sites, including bone metastases (10% vs. 0%) and liver metastases (approximately 25% vs. <10%), suggesting a heavier disease burden and worse prognosis at baseline.
04 Efficacy Data: 1-Year PFS and Response Durability
In the Intention-to-Treat (ITT) population, the CYTOSHRiNk study did not meet its primary endpoint:
- PFS Analysis: Median PFS was 6.3 months in the experimental arm versus 10.2 months in the control arm (HR = 1.2). The 1-year PFS rate was 35% for the experimental arm compared to 47.9% for the control arm.
- Per-Protocol (PP) Population: Among patients who successfully completed all four cycles of Nivo+Ipi, the median PFS improved to 11.5 months in the experimental arm (vs. 13.7 months in the control arm, HR = 1.07).
- Subgroup Analysis: In IMDC intermediate-risk patients, the median PFS in the experimental arm was numerically superior to the control arm (11.3 months vs. 10.0 months).
- ORR and Quality of Response: While ORRs were comparable (32.5% vs. 41.7%, all partial responses), the experimental arm showed superior durability of response. At the last data cutoff, 50% of responders in the experimental arm had ongoing responses, compared to only 10% in the control arm.
05 Safety: No Added Toxicity Risks
Safety data indicated that adding early cytoreductive SBRT to dual immunotherapy is feasible and safe:
- Adverse Events (AEs): The incidence of Grade ≥3 treatment-related AEs was similar between both arms. No new safety signals related to the combination of radiotherapy and immunotherapy were identified.
- Renal Function: There was no significant difference in the incidence of acute kidney injury (AKI), confirming that SBRT effectively preserved residual renal function.
Conclusion and Outlook
Dr. Lalani concluded that CYTOSHRiNk is the first randomized trial to evaluate the addition of upfront cytoreductive SBRT to first-line Nivo+Ipi. Although the 1-year PFS rate did not improve in the ITT population—likely driven by baseline risk imbalances—the study robustly demonstrated the safety of the regimen and its potential efficacy in specific subgroups, such as intermediate-risk patients and those completing full-course therapy.
Follow-up for OS, quality of life, and correlative biomarker analyses (including the microbiome) is currently ongoing. These findings provide a vital foundation for future investigations into the optimal integration of local ablative therapies with systemic immunotherapy in metastatic renal cell carcinoma.
