S100A16 and breast carcinoma: This report describes three major findings: 1) S100A14 and S100A16 expression is correlated to poor prognosis in breast cancer patients; 2) The localization of these proteins is limited to the plasma membrane along the lateral surface of the cell, which may be due to their interaction with actin; and 3) S100A14 and S100A16 promote the invasive activity of breast cancer cells.