To compare the efficacy and safety of ASP3550 to goserelin acetate in patients with prostate cancer.

This study consists of two parts. The purpose of PART 1 is to test non-inferiority of ASP3550 to goserelin acetate with respect to the cumulative castration rate in terms of serum testosterone when ASP3550 or goserelin acetate is administered for one-year in patients with prostate cancer.

The patients assigned to receive ASP3550 and completed the treatment in PART 1 are eligible for the treatment in PART 2, and will receive ASP3550 maintenance dose subcutaneously for additional term. The long-term safety, efficacy and PK of the continued ASP3550 treatment will be assessed in PART 2.

Inclusion Criteria:

• Male patient with histologically confirmed prostate cancer (adenocarcinoma).
• Patient in whom endocrine treatment is indicated. Patient having undergoing prostatectomy or radiotherapy with curative intention and has a rising serum PSA (PSA ≥ 2 ng/mL at screening) may be included.
• Has a serum testosterone level above 2.2 ng/mL at screening.
• Has an Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) score of 0 to 2 at screening.
• Has a serum PSA ≥ 2 ng/mL at screening.
• Has a life expectancy of at least 12 months.

Exclusion Criteria:

• Previous or present endocrine treatment for prostate cancer. Example: surgical castration, GnRH agonists, GnRH antagonists, antiandrogens or oestrogens, and 5α-reductase inhibitors.
• Received a 5α-reductase inhibitor within 25 weeks preceding screening.
• Is a candidate for curative therapy, i.e., radical prostatectomy or radiotherapy within 12 months.
• Has concurrent or a history of poorly controlled severe asthma, anaphylactic reactions, severe urticaria or angioedema.
• Has hypersensitivity towards mannitol.
• Has a marked prolongation of QT/QTc interval (two consecutive increases to >450 ms in QTc interval at retest) at screening.
• Has concurrent or a history of a disease (heart failure, hypokalemia, a family history of QT prolongation syndrome, etc.) that may induce Torsade de Pointes.

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.