Results from the phase 2 CYTOSHRINK trial show that adding Stereotactic Body Radiation Therapy (SBRT) to the immunotherapy combination of nivolumab and ipilimumab does not improve outcomes for patients with newly diagnosed advanced renal cell carcinoma (RCC). In fact, progression-free survival was shorter in the SBRT group (6.3 months) compared with immunotherapy alone (10.2 months). The 12-month progression-free survival rate and response rate were also lower in the SBRT arm. Overall survival data are still immature, but one-year survival was numerically higher in the immunotherapy-only group.
Researchers noted that patients in the SBRT group had more aggressive disease at the start of the study. More patients had advanced T3/T4 tumors, liver metastases, and larger primary tumors, which may have negatively affected results. These imbalances could partly explain why the radiation group performed worse.
In terms of safety, adding SBRT was generally manageable. Severe side effects occurred slightly more often in the SBRT arm, but treatment-related adverse events were similar between groups. Overall, the study does not support routinely adding SBRT to first-line immunotherapy for advanced RCC.