Chromosomal imbalances in small cell carcinomas of the urinary bladder

Small cell carcinomas (SCCs) represent a rare histological subtype of urina ry bladder cancer. Little is known abut the genetic alterations in these tu mours, To identify chromosomal aberrations that are typically present in SC C of the urinary bladder, ten tumours were analysed by comparative genomic hybridization (CGH), CGH allows screening for all relative DNA copy number gains and losses present in a tumour. SCCs of the bladder were characterize d by a high number of genomic alterations (mean: 11.3 per tumour). Deletion s were most frequent at 10q (7 of 10 tumours deleted), 4q, 5q (5/10 each), and 13q (4/10). These regions may carry tumour suppressor genes with releva nce for this particular tumour type. Gains of DNA sequences were most preva lent at sq (5/10), 5p, 6p, and 20q (4/10 each). High level amplifications w ere found at 1p22-32, 3q26.3, 8q24, and 12q14-21, These loci may pinpoint t he localization of oncogenes with relevance for small cell bladder cancer. The analysis of one tumour having areas of both SCC and transitional cell c arcinoma strongly suggests that SCC can develop from TCC through the acquis ition of additional genetic alterations. Copyright (C) 1999 John Wiley & So ns, Ltd.