Defining The Dna Damage Repair (Ddr) Genomic Landscape Of Urothelial Carcinoma Of The Bladder (Ucb).

502Background: Impaired DDR is associated with response to platinum-based chemotherapy. Several genomically directed trials have been proposed using DDR alteration status for enrolment. In this study, we characterized the deleterious DDR alteration (DDRa) landscape of UCB across various clinical states. Methods: Targeted exon capture and sequencing of at least 341 cancer-associated genes was performed prospectively on 451 UCB specimens (MSK-IMPACT assay). We assessed sequencing data for deleterious alterations in 34 genes representing canonical DDR pathways. Deleterious alterations included truncating mutations, homozygous deletions, and functionally validated missense mutations. Results: Table 1. In NMIBC, deleterious DDRa were enriched in high-grade disease ([39/136, 28.7%] high grade vs. low-grade [2/28, 7.1%]; p=0.02). The frequency of deleterious DDRa in chemo-naive MIBC was enriched relative to unmatched post-neoadjuvant chemotherapy (NAC) residual MIBC ([33/112, 29.5%] vs. [8/55, 14.5%]; p=0.01). P...