PTK2 and triple-negative breast carcinoma: Our result indicated that concomitant expression of β4 integrin and FAK occurred in triple-negative breast cancer tissues (Fig. 6b and Supplementary Fig. S5b), in that approximately 56% (27 out of 48) of the tumors displayed high levels of both β4 integrin and FAK, whereas approximately 17% (8 out of 48) of the tumors expressed only low levels of both proteins.