Epidermal growth factor-related peptides in the pathogenesis of human breast cancer

A number of different epidermal growth factor (EGF)-related peptides such as EGF, transforming growth factor α (TGFα), amphiregulin (AR), heregulin (HRG), and cripto-1 (CR-1), are coexpressed to varying degrees in both normal and malignant mammary epithelial cells. However, in general the frequency and level of expression of TGFα, AR, and CR-1 are higher in malignant breast epithelial cells than in normal mammary epithelium. In addition, several of these peptides such as TGFα and AR can function as autocrine and/or juxtacrine growth factors in mammary epithelial cells, and their expression is stringently regulated by mammotrophic hormones such as estrogens, activated proto-oncogenes that have been implicated in the pathogenesis of breast cancer, and other growth factors. The redundancy of expression that is observed for a number of these structurally related peptides in both normal and malignant mammary epithelial cells suggests that some of these peptides may be involved in regulating other aspects of cellular behavior such as differentiation in addition to proliferation.