Inclusion Criteria:

- Histologically proven prostate cancer (adenocarcinoma) of all stages

- A patient in whom endocrine treatment is indicated. Patients with rising serum PSA
after having prostatectomy or radiotherapy performed with curative intention

- Serum testosterone level above 2.2 ng/mL

- An ECOG (Eastern Co-operative Oncology Group) P.S. (Performance Status) score of 0 to
2

- Serum PSA level above 2 ng/mL

Exclusion Criteria:

- Previous or present endocrine treatment for prostate cancer. However, patients who
have undergone neoadjuvant/adjuvant endocrine therapy for a maximal duration of 6
months and in whom prostatectomy or radiotherapy was terminated at least 6 months

- Treated with a 5α-reductase inhibitor

- A candidate for curative therapy, i.e., radical prostatectomy or radiotherapy within
12 months

- Concurrent or a history of severe liver disease

- Abnormal ECG such as long QTc

- A patient receiving ASP3550 in past times

- Administered drug in another clinical study or a post-market clinical study in the 28
days prior to the study