Immunohistochemical analysis of PDK1 expression in breast cancer.

3-phosphoinositide-dependent protein kinase-1 (PDK1) functions downstream of phosphoinositide 3-kinase (PIK3) and activates members of the AGC family of protein kinases that are known to play crucial roles in physiological processes associated with cell metabolism, growth, proliferation and survival. Changes in the expression and activity of PDK1 and several AGC kinases have been linked to human disease, including cancer.,We used immunohistochemical analysis to determine PDK1 expression in 241 tumors from patients with breast cancer in which we had previously analyzed PIK3CA mutation status.,Moderate or high expression of PDK1 was observed in 213 of the 241 cases (88%). There was no correlation between PIK3CA mutation status and PDK1 overexpression.,Our findings indicate that PDK1 is independently activated in breast cancer and not only as part of the PIK3CA pathway, suggesting that PDK1 plays a specific and distinct role from the canonical PIK3/Akt pathway and promotes oncogenesis independently of AKT. Our data implicate PDK-1 and downstream components of the PDK-1 signaling pathway as promising therapeutic targets for the treatment of breast cancer.