Cytogenetic studies and spectral karyotyping have shown chromosome 1 to be frequently involved in rearrangements in ovarian tumors [1-5]. Howev­er, specific genes in chromosome 1, of importance for ovarian carcinogenesis, are still not identified. To elucidate the mechanism of carcinogenesis, de­tailed analysis of gene amplifications and deletions in different cancers is needed. Comparative genom-ic hybridization (CGH) was introduced in 1992 for identifying DNA copy number changes in different types of tumors with a resolution, higher than that of chromosomal analysis, but of not more than 5-10 Mb [6]. The CGH studies showed its efficiency for discovering the regions involved in carcinogenesis, and eventually for determining their diagnostic and prognostic significance [7]. The CGH analysis of ovarian tumors resistant to standard platinum-based chemotherapy revealed that genetic gain of 1q21-q22 is the most common alteration present [8]. This showed that there are different genetic changes in different groups of tumors and transfer efforts of investigation to analysis of alterations in chromo­some 1, which may be of importance for the clinical course of the disease.

Consistently higher transcription activity in a new large region of the long arm of chromosome 1 [1q21-q23 (140-160 Mb)] was established in many malignant, including ovarian tumors. For identifi­cation of the most common amplified loci of 1q in ovarian tumors, real time polymerase chain reac­tion (PCR) of 10 gene loci on this arm showed that MUC1 was the most frequently amplified of them and significantly more often in platinum-resistant ovarian tumors (92%) compared to well responsive tumors (21%) [9]. Aberrations involving the region 1q21 have been found in ovarian tumors [10]. These findings increased the scientific interest in analysis of this region using specific gene probes. We inves­tigated the frequency of copy number changes of two specific BAC (bacterial artificial chromosomes) clones in 1q21.3 and 1q23.3 in a large number of ovarian tumors of different malignancy, histology, stage and grade, and correlated these with tumor phenotype.