ERBB2 and breast cancer: This may be due to the hyper-activation of p38 MAPK in these Her2/neu-overexpressing cells (6.5-fold elevated phosphorylation compared with control cell line), which has reached a maximum for its stimulatory effect on cell invasion such that further elevation of p38 activity beyond the maximum does not necessarily lead to further increase in the invasive potential of these already highly invasive breast cancer cells.