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). Here, PGR is linked to breast carcinoma.