Molecular cytogenetic analysis of a nontumorigenic human breast epithelial cell line that eventually turns tumorigenic: validation of an analytical approach combining karyotyping, comparative genomic hybridization, chromosome painting, and single-locus fluorescence in situ hybridization.

The immortalized, nontumorigenic human breast epithelial cell line HMT-3522 has been used as a model for premalignant and, eventually, malignant development. During cultivation, the karyotype evolution was followed. At an early stage, a very long constant phase showed a near-diploid karyotype, with only five marker chromosomes. DNA from this phase was used for comparative genomic hybridization (CGH) analysis, confirming a previously known MYC amplification, and the integration sites were subsequently determined by single-locus fluorescence in situ hybridization (FISH). Furthermore, gains of 5q22-qter and 20q11-qter and deletion of most of chromosome 6 (6p23-qter) were detected by CGH. Because of uncertainty about some of the indicated changes, including a deletion of Ip35-pter, the CGH findings were investigated more closely by chromosome painting, leading to a revision of the karyotype: 45,XX,del(I)(p35),-6,dup(8)(pter-->qter::qter-->q24),der(12) t(6;12)(p23; p13),der(14)t(5;14)(q22;q32.3),der(17)t(8;17;20)(17pter-->17q25 ::8qter--> 8q23::8q24-->8qter::8q24-->8qter:: 8q23-->8q24.1::20q11-->20qter). Some karyotypic changes were confirmed by CGH; others had to be revised; and, in the Ip35 region, classical cytogenetics seems superior to CGH. However, CGH revealed a karyotypically unsuspected dup(20q) that might be of special relevance to breast tumor initiation or progression. Our study confirms that CGH is supplementary to current technologies, e.g., karyotyping and Southern analysis, but cannot replace them. In addition, our cell line turned out to be an excellent model for comparison among the different methods. The results imply that future cytogenetic analyses of complex karyotypes should be based on a combination of karyotyping, CGH, and FISH.