[Different coexisting genotypes in the breast cancer cell line MDA-MB-468].

Intratumor genetic heterogeneity, a well-known characteristic of numerous cancers, often confounds a precise diagnosis and leads to therapy resistance. This study deals with such chromosomal variability, which may be due to an inherent genetic instability affecting heterogeneity and clonal effects. Subpopulations of the breast cancer cell line MDA-MB-468 were isolated according to epidermal growth factor receptor (EGFR) expression by FACS. Whole genome profiling (CGH; mapping arrays) and determination of egfr gene amplification (fluorescence in situ hybridisation, FISH; qPCR) were done directly after sorting or after several passages of cell culture. Subpopulations differed in the amplification of the egfr-locus 7p11-14 showing egfr gene amplification rates of up to 60-fold in high-level expressing populations and less than 2-fold in low-level expressing populations. However, after several passages the original low-level cells showed a new amplification of the egfr gene, which was as heterogeneous as the original amplification detected in MDA-MB-468. Additional, spontaneously expressed fragile sites could be shown in FISH analyses which may affect cell culture heterogeneity. Understanding the precise chromosomal process would clarify mechanisms in vivo and improve both diagnosis and therapy of corresponding cancers.