PD42-05 FECAL MICROBIOTA PROFILING OF PATIENTS TREATED WITH NEOADJUVANT PEMBROLIZUMAB FOR MUSCLE INVASIVE UROTHELIAL CARCINOMA

Abstract

INTRODUCTION AND OBJECTIVE: Immunotherapy (IO) by immune checkpoint inhibitors (ICIs) is effective in metastatic urothelial carcinoma (UC) and showed promising activity in muscle-invasive and non-muscle invasive UC of the bladder. Among the potential determinants of IO efficacy, the immunomodulatory effect played by the gut microbiota has been increasingly studied, to the point that microbial “signatures” associated with response to therapy have been described. In our study, we aimed to study the fecal microbiota in patients undergoing neoadjuvant IO for muscle-invasive UC. METHODS: Pre-IO stool specimens were available for analysis from 42 patients enrolled in the PURE-01 trial (NCT02736266), testing 3x200mg flat-dose pembrolizumab every 21 days before radical cystectomy (RC). 16s sequencing and analysis were performed using standardized protocols, using mock communities and DNA standards (ZymoBIOMICS) to control for potential extraction and sequencing contaminations. Complete response (CR) to neoadjuvant IO was defined as ypT0N0 in RC specimens, while partial response (PR) was defined as