298 Background: The type and frequency of recurrent, targetable alterations in muscle-invasive, treatment-naïve urothelial cancer (UC) have been well-catalogued through the bladder TCGA. We sought to validate these findings within a prospective cohort of patients (pts) with progressive UC treated at our institution. This cohort typifies the UC patient population managed by medical oncologists. Methods: Pts with a diagnosis of UC were enrolled onto an IRB-approved protocol between 1/14/14 and 7/29/14, which allowed for sequencing of all exons in 341 oncogenes and tumor suppressor genes using an exon capture next generation sequencing assay (NGS) platform (MSK-IMPACT) in a CLIA lab from tumor and matched germline DNA. Somatic point mutations, truncations, copy number alterations, and insertions/deletions were detected. Results: 49 UC pts were sequenced, 5 (10%) having upper tract disease. 33 (67%) tumors were pure UC histology with the remainder containing divergent differentiation. 17 samples (24%) were metastatic in origin, and 40 samples were analyzed from pts who had received prior chemotherapy. The most common alteration identified was point mutations within the TERT promoter (71%), a region not sequenced by TCGA. Additional alteration frequencies were similar between both sets. FGFR3 mutations overlapped with both PIK3CA and TSC1 alterations and co-alterations were observed between FGFR3 and CDKN2A as well as PIK3CA and CCND1. Conclusions: TERT promoter mutations were found at high frequency in the MSK-IMPACT tumor cohort. The frequency and type of alterations identified in the bladder TCGA are similar to the MSK-IMPACT cohort, suggesting that TCGA data can be used to guide clinical trials in the metastatic, pre-treated population. Overlap of alterations within and across core signaling pathways underscores the need for functional validation of alterations and for rational combinations of targeted therapies to effectively treat advanced UC. [Table: see text]