PDK1 and breast cancer: As a major kinase of the AGC protein kinase family, 3-phosphoinositide-dependent protein kinase 1 (PDK1) has played crucial roles in various cellular process via the PI3 K/AKT-dependent or PI3 K/AKT-independent pathway in BC cells, such as tumorigenesis, growth and survival, metastasis, tumor microenvironment (TME) regulation, and drug resistance.