As the cancer mutates to become castrate resistant, it may be because the cancer produces its own androgens. Androgen deprivation therapy does not get inside the cancer cell to prevent this. Those tumor androgens need to bond to a receptor to have an effect. Enzalutamide (Xtandi®) is a prescription medicine newly approved to treat men with castration-resistant prostate cancer that works by blocking the androgen receptor. Xtandi does get inside the tumor cells to take effect. Xtandi is taken orally—four capusles once a day with or without food. It does not need to be taken with prednisone. The drug is very safe, but there is always the potential for side effects. Many patients experience fatigue, some have upset stomachs or other GI side effects, and it can worsen high blood pressure. An extremely rare event is a seizure, but it is not clear in the clinical studies if the drug really caused this or not.
A large scale clinical trial was conducted to evaluate the effectiveness and safety of the Xtandi capsule . Of the 1,199 men in the study, 800 were given Xtandi and 399 were given a placebo (capsule containing no active medication). The main objective of the study was to measure overall survival. Results of this clinical study showed that men taking Xtandi lived longer than men taking placebo. Radiology tests showed tumors shrink and the PSA went down with treatment.