To find effective doses of ASP3550 on the maintenance of serum testosterone suppression in patients with prostate cancer.

ASP3550 is administered periodically to patients with prostate cancer. The primary efficacy variable is the effect of ASP3550 on the maintenance of serum testosterone suppression. In addition, the safety and pharmacokinetics of ASP3550 will be investigated.

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

Access to anonymized individual participant level data collected during the study, in addition to study-related supporting documentation, is planned for studies conducted with approved product indications and formulations, as well as products terminated during development. Studies conducted with product indications or formulations that remain active in development are assessed after study completion to determine if Individual Participant Data can be shared. Further details on Astellas' data sharing policy can be found at https://www.clinicaltrials.astellas.com/transparency/.

Access to participant level data is offered to researchers after publication of the primary manuscript (if applicable) and is available as long as Astellas has legal authority to provide the data.

Researchers must submit a proposal to conduct a scientifically relevant analysis of the study data. The research proposal is reviewed by an Independent Research Panel. If the proposal is approved, access to the study data is provided in a secure data sharing environment after receipt of a signed Data Sharing Agreement.