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Overexpression of the c‐erbB‐2 protein in human breast tumor cell lines

The c‐erbB‐2 proto‐oncogene is amplified in a high percentage of primary human breast tumors, suggesting that the overexpression of this gene may be involved in the development of human breast cancer. We have investigated five human breast tumor cell lines and have detected amplified c‐erbB‐2 gene copies in two of them. This amplification leads to overexpression of the c‐erbB‐2 protein. In addition, two other cell lines have elevated protein levels without gene amplification, suggesting that other mechanisms can lead to overexpression of the c‐erbB‐2 protein. These results are similar to those that we obtained during a study of primary breast tumors (Berger et al.: Cancer Res 48:1238–1243, 1988). These breast tumor cell lines should be useful for an analysis of c‐erbB‐2 expression and of the mechanisms that in some cases lead to overexpression.