Aggressive prostate cancer can occur under a low DHT level environment where the prostate cancer of a low malignancy with high DHT dependency cannot easily occur. Aggressive prostate cancer can produce DHT from adrenal androgens more autonomously than non-aggressive prostate cancer does under low testosterone environment with conventional ADT. These locally produced androgens can play important roles in the pathogenesis and development of prostate cancer. Androgen receptor (AR) signaling pathway is an important mechanism in proliferation of aggressive prostate cancer during ADT. AR transcriptional activity is reactivated in castration-resistant prostate cancer (CRPC) and identifies the intracellular conversion of adrenal androgens to testosterone as a mechanism mediating this reactivation. Recently, encouraging early phase trial results of promising ADT agents for the patients of CRPC have been reported. Abiraterone acetate, an irreversible inhibitor of 17alpha-hydroxylase/C17,20-lyase (CYP17), is well tolerated and has significant and durable anti-tumor activity both in patients with chemotherapy-naive prostate cancer and in docetaxel-treated patients with CRPC. MDV3100 is a small-molecule, pure AR antagonist that inhibits AR nuclear translocation and DNA binding. New ADTs using CYP17 inhibitors such as abiraterone acetate and AR antagonists such as MDV3100 for patients with CRPC will break through the limitation of the efficacy of conventional ADTs that have been used for nearly 70 years. Therefore, it is important to examine the status of in situ androgen metabolism and/or synthesis in detail in order to improve the clinical response to ADT in patients diagnosed with biologically aggressive prostate cancer from now on.