PTK2 and cancer: Taking into account that RA exerts its effects via RARs and that Src-FAK are critical proteins involved in cancer progression, we initially explored the expression profiles of RARA, RARB, RARG, SRC, and PTK2 in different types of human BC cells (T-47D, MCF7, ZR75.1, BT-474, SK-BR3, MDA-MB-468, and MDA-MB-231) and a normal breast cell line (MCF-10A).