The influence of Clostridium butyricum CBM 588, a commensal probiotic previously shown to elicit anti-tumor effects in murine models of bladder cancer [90], will be evaluated on microbiome and immune parameters of patients with renal cell carcinoma at various stages, those treated with PD-1 blockade and a small-molecule inhibitor of tyrosine kinases (cabozantinib) (NCT05122546), and on patients with advanced kidney cancer receiving anti-CTLA-4/anti-PD-1 combination therapy (NCT03829111). The gene discussed is PDCD1; the disease is kidney cancer.