ST14 and breast cancer: This is in line with the increased Matriptase activity formerly reported for breast cancer cells (which have largely lost their epithelial polarity) in comparison to untransformed MCF-10A breast epithelial cells [9], and with our data obtained in zebrafish embryos, where loss of the epithelial cell polarity regulators atp1b1a and lgl2 both promote Matriptase-mediated pre-neoplastic processes (Figs 1 and 7).