Gut microbiome composition and response to sunitinib in metastatic renal cell carcinoma (mRCC).

657Background: Recent evidence supports a link between stool microbiome composition and immunotherapy response. However, it is unclear how the microbiome may influence clinical outcome in mRCC where vascular endothelial growth factor-targeted therapies remains a standard of care. Methods: Five consecutive stool samples were collected at baseline and at weeks 2, 3, 4 and 12 of treatment with sunitinib in patients (pts) with mRCC. In responders (R: complete/partial response and stable disease) and non-responders (P: primary progression), gut microbiota composition was assessed through extraction of microbial DNA where 16s RNA gene tags (v4) were generated by PCR amplification and sequenced using MiSeq (Illumina). Sequence reads were processed by Mothur software, assembled in Operational Taxonomic Units (OTUs), taxonomically annotated to the genus level, and used to construct Bray-Curtis dissimilarity matrix. The similarity of samples was visualized by principle coordinate (PCo) analysis and further confirme...