Characterization Of Genomic Alterations As Biomarkers Of Immune Checkpoint Inhibitor (Ici) Response In Metastatic Urothelial Carcinoma (Muc).

400Background: ICIs have expanded therapeutic options for mUC patients (pts); however, biomarkers such as PD-L1 have not served as reliable predictors of treatment efficacy. High tumor mutation burden (TMB) has been previously described as a potential biomarker for predicting ICI response in several indications, but its utility is still being explored in mUC. Here, we compare the genomic landscapes and clinical outcomes of mUC pts following ICI therapy using an investigational solid tissue-based next-generation sequencing assay to assess TMB and identify genetic correlates of ICI response. Methods: 20 pts with mUC treated with ICIs at Duke Cancer Institute were identified. Tumor samples were retrospectively evaluated with a Personal Genome Diagnostics Assay for somatic variants across u003e 500 genes, as well as TMB and microsatellite status. Tumor samples were also stained for PD-L1 status using the Dako 22C3 IHC assay. Deidentified clinical information was extracted from the medical record and tumor respons...