Alterations in genes regulating cell cycle and apoptosis in high-grade urothelial carcinoma.

Abstract

237 Background: Dysregulations of cell cycle and inhibition of apoptosis are crucial factors in tumorigenesis of multiple malignancies, including urothelial carcinoma (UC). Deletions of TP53 and CDKN2A and amplification of MDM2 have been observed in UC, but their exact frequency and functional consequence is less known. We sought to determine the frequency of copy number alteration (CNA) and mutations of genes that regulate cell cycle or apoptosis in a panel of 96 cases of high-grade UC (HGUC) of bladder. Methods: 96 frozen cases of HGUC were studied, including 11 bladder small cell carcinomas. DNA was isolated and analyzed for CNA by comparative genomic hybridization (CGH) using a one million oligonucleotide probe array from Agilent. The targeted genes included TP53, MDM2, CCND1, CCNE1, CDKN2A/B, E2F3 and Rb1. Traditional Sanger sequencing for mutations within TP53, Rb1, and CDKN2A was also performed. Results: The frequency of CNA and mutations are listed in the table. Overall, 54 of 96 cases (56%) showed CNA (45) or mutation (13). Deletion of CDKN2A/B and amplification of E2F3 were the most common alterations in cell cycle regulatory genes (13 cases each, 14%), followed by amplification of CCND1 (11 cases, 11%). There was no co-amplification of CCND1 and CCNE1 in any sample. Rb1 deletion was present in five cases. CNA in E2F3 and Rb1 were mutually exclusive in 14 of 16 cases (88%) and were both present in two cases only. Mutations in TP53 were noted in 13 cases and deletions in nine. Amplification of MDM2 was noted in four cases, none of which overlapped with TP53 deletions or mutations. Overexpression of E2F3 was significantly more common in small cell carcinoma (5/11) compared to conventional UC (8/85, p = 0.006). Conclusions: Regulators of cell cycle and apoptosis are amplified, deleted or mutated in more than half of cases (56%) of high-grade urothelial carcinoma. The overwhelming majority of these abnormalities are nonoverlapping. Amplification of E2F3 seems to be overrepresented in small cell carcinoma of bladder. [Table: see text] No significant financial relationships to disclose.