ERBB2 and breast carcinoma: To further investigate the role of PYK2 in proliferation and invasion of HER2+/ER−/PR- breast cancer cells, we performed mass spectrometry analyses of protein extracts from untreated control (pLKO.1 empty vector) and untreated and treated PYK2 knockdown SkBr3 cells (Fig. 4a and b).