INTRACELLULAR COEXPRESSION OF EPIDERMAL GROWTH-FACTOR RECEPTOR, HER-2NEU, AND P21(RAS) IN HUMAN BREAST CANCERS - EVIDENCE FOR THE EXISTENCE OF DISTINCTIVE PATTERNS OF GENETIC EVOLUTION THAT ARE COMMON TO TUMORS FROM DIFFERENT PATIENTS/

Multiparameter flow cytometry studies were performed on cells from the primary tumors of 94 patients with breast cancer. Correlated cellular measurements of cell DNA content, Her-2/neu, epidermal growth factor receptor (EGFR), and p21(ras) levels were performed on each of 5,000 t o 100,000 cells from each tumor. When criteria for positivity were mat ched with those in common use for immunohistochemical studies, 28 of 9 4 (30%) breast cancers were classified as positive for Her-2/neu overe xpression. When similar criteria were applied to the EGFR measurements , 23 of 94 (24%) cases were classified as positive for EGFR overexpres sion. Similarly, 23 of 94 (24%) cases mere classified as positive for p21(ras) overexpression. By conventional flow cytometric criteria for DNA ploidy, 24 cases mere diploid, 28 were tetraploid, and 42 were ane uploid. When the measurements were treated as separate sets of data, t he only statistically significant correlations noted were the high fre quency of diploid tumors, which did not overexpress any of the three o ncogenes studied (P < 0.05), and an association between Her-2/neu over expression and aneuploidy (P < 0.03). When the data were treated as co rrelated intracellular measurements, 90 of the 94 tumors studied conta ined a population of cells in which the intracellular levels of Her-2/ neu expression were directly correlated with the levels of EGFR expres sion in the same cells. The ratio of Her-2/neu molecules to EGFR molec ules in the same cells exceeded 1 in the majority of tetraploid and an euploid cases and was close to or less than 1 in the majority of diplo id cases. In nearly all tumors, p21(ras) overexpression was observed o nly in cells that overexpressed Her-2/neu, EGFR, or both, and p21(ras) levels per cell were more closely correlated with levels of EGFR per cell in the same cells than with Her-2/neu levels per cell. The data a re consistent with a model in,which heterodimerization of Her-2/neu an d EGFR in individual cells is achieved by one of several genetic evolu tionary pathways, all of which commonly lead to p21(ras) overexpressio n. The two major genetic evolutionary pathways identified in this stud y are an aneuploid, Her-2/neu overexpression-driven pathway seen in 59 of 94 tumors, and a diploid, EGFR overexpression-driven pathway seen in 19 of 94 tumors. All tumors with Her-2/neu:EGFR ratios greater than 2 contained an infiltrating ductal carcinoma component, whereas all i nfiltrating pure lobular carcinomas had Her-2/neu:EGFR ratios that wer e less than 2. All of the genetic evolutionary pathways identified in this study mere represented among the 11 tumors from patients who expe rienced early tumor recurrences.