A drug used to treat prostate cancer that is castration resistant (has not responded to treatments that lower testosterone levels). Enzalutamide binds to proteins called androgen receptors, which are found in some prostate cancer cells. These proteins bind to androgens (male hormones) and may cause cancer cells to grow. Enzalutamide blocks these proteins and may keep cancer cells from growing. It is a type of antiandrogen. Also called Xtandi.