The antiandrogen withdrawal syndrome was first reported in patients with prostate cancer who manifested disease progression after total androgen blockage therapy with medical or surgical castration and pure antiandrogen, flutamide; discontinuation of flutamide resulted in a decline in prostate specific antigen and, in some cases, with clinical response. Same phenomena have been reported after the withdrawal of casodex, chlormadinone acetate, megestrol acetate, diethylstilbestrol, and estramustine phosphate. Mutations in the androgen receptor(AR) gene were discovered in clinical specimens of human prostate cancer patients who showed this syndrome and some of these being identical to the mutation found in LNCaP prostate cancer cell line. Another mechanism otherwise the point mutation of AR would be also speculated.