Comparative genomic hybridization (CGH) is a powerful technique for the quantitative detection of changes in chromosome copy number (1 -3 ). It offers an advantage over conventional cytogenetic techniques in the analysis of tumor karyotypes through its utilization of DNA as the material of study, thus avoiding the problems associated with obtaining good quality metaphases from tumor material. Though CGH is not sensitive to balanced chromosomal rearrangements and changes in DNA ploidy, it can be sensitive to twofold differences in chromosome copy number, making identification of mono- and trisomic karyotype straightforward. Furthermore, deletions and amplifications as small as 2 Mb can be detected, and identification of such regions by CGH analyses of ovarian cancers (4 -6 ) have already contributed to the identification of the putative oncogene PIK3CA (7 ).