Chromosomal markers of immortalization in human breast epithelium.

We describe a series of five immortal breast cell lines that have emerged independently from diploid cultures from two individuals. We have karyotyped representative cultures of each of these lines prior to and at intervals after immortalization. Although considerable diversity of chromosomal aberration was found among the five lines, analysis of sublines has defined the chromosomal changes common for each immortalization. These changes differed both within and between the individual patient sources. Some common alterations were noted in lines from both patients, however, including loss of the short arm of chromosome 20 and gain of 1q. We suggest that genes within these chromosomal regions contribute to spontaneous immortalization of human breast epithelium.