SLC9A1 and breast cancer: Previous investigations in MCF7 human breast cancer cells support the functional consequences of NHE1 observed in our human breast cancer cohort: NHE1 protein expression in the MCF7 cells markedly increased during heterologous overexpression of an amino-truncated ErbB2 receptor (Lauritzen et al., 2010), yet pharmacological inhibition of NHE1 under these conditions stimulated cell migration (Lauritzen et al., 2012).