Abstract 1749: Stability of copy-number profiles defines two molecular subtypes during urothelial carcinoma’s evolution

Abstract

Abstract Background: Somatic copy-number alterations (SCNAs) are distinct molecular events occurring in muscle-invasive urothelial carcinoma (UC). Defining the biologic role and the timing of SCNAs in UC’s evolution is critical for understanding disease biology and for precision therapy. Methods: To examine whether distinct SCNAs define specific subtypes of UC and characterize the evolutionary dynamics of SCNA acquisition, we conducted whole-exome sequencing (WES) of a discovery cohort of 44 advanced UC tumors and matching germline samples, including 13 pairs of matched primary and metastatic tumors prospectively collected before and after chemotherapy. We queried WES data from 285 UCs from The Cancer Genome Atlas (TCGA) as a validation cohort. We performed a novel in-depth allele-specific copy-number analysis in 2503 cancer genes using the CLONET computational framework, which accounts for tumor ploidy and cellularity to infer the clonal hierarchy of SCNAs. Results: Analysis of SCNAs from tumor pairs within each patient revealed punctuated evolution of SCNAs occurring early in UC’s development followed by minor changes (clonal stasis) throughout the tumor’s lifetime. Two distinct clusters of UCs with strikingly different SCNA profiles in the discovery cohort emerged. Cluster A was defined by diploid copy number background and focal deletions in the 9p21 region (CDKN2A, CDKN2B and MTAP). Cluster B was defined by genome-wide duplications and several enriched amplifications including 1q21.1 (SETDB1 and MLLT11), (P = 0.0002) and 6p22.3 (E2F3), (P = 0.001). TP53 mutations (P = 0.0001) were enriched in the cluster B, consistent with the role of functional p53 as a “guardian of the genome” preventing chromosomal instability. SCNAs clusters A and B were confirmed in the TCGA validation cohort. Cluster A was enriched with tumors belonging to TCGA bladder cancer cluster III (“basal/squamous-like”) (P = 0.02). Conclusions: Using novel allele-specific SCNAs analysis, we define two distinct clusters of UC presenting a framework for understanding this aspect of UC’s biology. In contrast to somatic mutations, SCNAs are clonally static during each tumor’s evolution. This data has important implications for precision medicine for UC. Citation Format: Bishoy M. Faltas, Davide Prandi, Scott T. Tagawa, David Nanus, Ana M. Molina, Himisha Beltran, Francesca Demichelis, Mark A. Rubin. Stability of copy-number profiles defines two molecular subtypes during urothelial carcinoma’s evolution [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1749. doi:10.1158/1538-7445.AM2017-1749