(UroToday.com) There have been transformational changes in first-line therapy for patients with advanced renal cell carcinoma (RCC) in the past three years. Foremost among these is the move from monotherapy to combination approaches. While CheckMate 214 first brought combination therapy with dual checkpoint inhibition to the forefront, subsequent studies have examined combinations of immune checkpoint inhibitors in the first-line setting. Recently, it has become apparent, through for example data regarding the use of concomitant antibiotics, that the gut microbiome is a potent mediator of immune checkpoint inhibitor (ICI) activity. In metastatic RCC, retrospective evidence suggests that both specific bacterial species and cumulative microbial diversity may contribute to treatment response. In particular, CBM-588, a live bacterial product from C. butyricum, can augment response to immune checkpoint inhibition in non-small cell lung cancer. In the Kidney and Bladder Poster Discussion session at the 2021 American Society of Clinical Oncology (ASCO) Annual Meeting, Dr. Meza presented the first results of a randomized controlled trial of nivolumab and ipilimumab with or without CBM-588.