Introduction
BRK is an intracellular protein-tyrosine kinase that is expressed in 60% of human breast cancers but is undetectable in normal and benign breast tissues. The introduction of the BRK gene into the normal breast epithelial cell lines HB4a and MCF10-A leads to a potentiation of their growth response to the mitogen EGF and their ability to proliferate in an anchorage-independent manner. BRK and the EGF receptor (EGFR) have also been shown to form a constitutive association in mammary epithelial cells.