DNA damage response (DDR) gene mutations (mut), mut load, and sensitivity to chemotherapy plus immune checkpoint blockade in urothelial cancer (UC).

300Background: Somatic mut in DDR genes have been associated with increased sensitivity to cisplatin in UC. Higher mut load has correlated with response to immune checkpoint blockade. We hypothesized that DDR mut result in higher mut load and DDR mut UC may be particularly sensitive to both chemotherapy and immune checkpoint blockade. Methods: Three cohorts were utilized: (1) TCGA UC cohort (n = 389), (2) Mount Sinai (MS) cohort (n = 67) of UC (cystectomy) specimens subjected to targeted exome sequencing for 341 genes (MSK-IMPACT), and (3) Phase 2 trial of gemcitabine, cisplatin, plus ipilimumab (GCI) in metastatic UC from which 28/36 enrolled patients (pts) had specimens suitable for whole exome sequencing. DDR mut were defined as somatic alterations in one of 52 genes. Deleterious (del) mut were defined as nonsense, frameshift, splice site, or hotspot point mut. Results: The mut load using all genes in the TCGA cohort, and restricted to the 341 IMPACT genes, were highly correlated (rs= 0.81, p < 0.001)....