LAUSR

584Background: Diarrhea occurs in ~50% patients with mRCC receiving VEGFTKIs, and is a common cause of VEGFTKI Rx dose reductions/delays/interruptions. Stool bacteroides level directly correlates with diarrhea in these patients on Rx with VEGFTKI (Pal SK, Clinical Cancer Research 2015, PMID:26152743). Hypothesis was that mRCC patients on incidental antibiotics (ABX) which also target stool bacteroides will have less diarrhea, leading to improved Rx compliance, and improved outcomes on VEGFTKI. Methods: A retrospective study of mRCC patients with MSKCC intermediate or poor risk mRCC on 1st line VEGFRTKIs between 2005-2017. ABX usage was categorized by ABX bacteroides sensitivity at anytime during Rx with 1st line VEGFTKI along with the total number of days on ABX. 1st line VEGFRTKI progression free survival (PFS) was assessed by Kaplan-Meier and Cox proportional hazard models. Results: 145 patients with intermediate (n = 123, 85%) or poor risk (n = 22, 15%) mRCC on a VEGFTKI were identified. ABX were presc...