Association of microbiome and plasma cytokine dynamics to nivolumab response in metastatic renal cell carcinoma (mRCC).

656Background: Checkpoint inhibitors (CPI) represent a standard of care in mRCC. The relationship of the microbiome to benefit from CPIs has been suggested in clinical studies in melanoma (Wargo et al ASCO 2017). Here we provide updated evidence of association between microbiome composition, plasma cytokines and response to nivolumab in mRCC patients (pts). Methods: Stool and blood samples were prospectively collected from pts with mRCC at 3 time points relative to nivolumab treatment (baseline, week 4 and week 12) and used to assess gut microbiota composition in two different groups: responders (R; including complete/partial response and stable disease) and non-responders (P; primary progression). For stool analyses, microbial DNA was extracted, 16s rRNA gene tags (v4) were generated by PCR amplification and sequenced using MiSeq (Illumina). Sequence reads were processed by Mothur software, assembled in OTUs, taxonomically annotated and used to construct dissimilarity matrices. Differentially abundant ta...