ERBB2 and breast cancer: In further support of a SNAI2-PEAK1 stromal cell signaling axis in breast cancer, we noted a significant positive correlation between SNAI2 and PEAK1 protein levels in the stromal compartment of breast cancer samples (Fig. 1f, g), and that these SNAI2 and PEAK1 protein levels were specifically expressed at higher levels within the stroma of HER2-positive tumors (Fig. 1h).