The metastasis-promoting protein S100A4 regulates mammary branching morphogenesis

► Expression of S100A4 in breast carcinoma cells is an independent marker of poor prognosis. ► The protein was mainly expressed in the stromal compartment of normal human breast tissue. ► S100A4 increased mammary gland branching phenotype and caused induction of MMP-3 expression. ► S100A4 expression contributed to a proteolytic and invasive phenotype in normal mammary epithelial cells.