[732] Molecular Genetic Abnormalities in Regulators of Cell Cycle and Apoptosis in High Grade Urothelial Carcinoma of Bladder.

Hikmat A Al-Ahmadie, Gopa V Iyer, Oscar Lin, Anuradha Gopalan, Samson W Fine, Yingbei Chen, Satish K Tickoo, Victor E Reuter, Bernard H Bochner, Dean F Bajorin, Matthew I Milowsky, David B Solit. Memorial Sloan-Kettering Cancer Center, New York, NY

Background: Cell cycle dysregulation and inhibition of apoptosis both drive tumorigenesis in multiple malignancies, including urothelial carcinoma (UC). Copy number alteration (CNA) is a well-known mechanism for dysregulation of these cardinal functions. Deletion of CDKN2A and TP53 and amplification of MDM2 has been observed in UC, but the exact frequency and functional consequence of such alterations is less known. We sought to define the frequency of amplification, deletion and mutations of genes that regulate cell cycle or apoptosis in a panel of 96 cases of high-grade UC (HGUC) of bladder.
Design: DNA was isolated from 96 frozen samples of HGUC (including 10 cases of small cell carcinoma of bladder) and analyzed for CNA through comparative genomic hybridization (CGH) using a 1 million oligonucleotide probe array from Agilent. The targeted genes included TP53, MDM2, CCND1, CCNE1, CDKN2A/B, E2F3 and Rb1. Traditional Sanger sequencing to screen for mutations within select genes (TP53, Rb1, and CDKN2A) was also performed.
Results: Table 1 depicts the frequency of CNA and mutations found within the studied genes.

Table 1. Copy number alterations and mutations in genes of cell cycle regulation or apoptosis

Gene	Abnormality (n)
CCND1	Amp (11)
CCNE1	Amp (4)
CDKN2A/B	Del (13), Amp (1), Mut (2)
E2F3	Amp (13)
RB1	Del (5), Mut (1)
TP53	Mut (12), Del (9)
MDM2	Amp (4)

Amp: amplification; Del: deletion; Mut: mutation

Overall, 54 of the 96 cases (56%) showed some CNA (45) or mutation (13). Deletion of CDKN2A/B and amplification of E2F3 were the most common CNA events identified within cell cycle regulatory genes, occurring in 13 samples each (14%), followed by amplification of CCND1 in 11 samples (11%). There was no co-amplification of CCND1 and CCNE1 in any of the samples. Rb1 deletions were observed in 5 samples. CNA in E2F3 and Rb1 were mutually exclusive in 14 of the 16 samples (88%) and were both present in 2 samples only. Mutations in TP53 were noted in 13 samples and deletions in 9 samples. Amplification of MDM2 was noted in 4 samples, 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 the bladder.
Category: Genitourinary (including renal tumors)

Monday, February 28, 2011 2:00 PM

Platform Session: Section A, Monday Afternoon