The primary objectives of this study are to investigate the safety and tolerability of BAY 1841788 in Japanese subjects with metastatic castration-resistant prostate cancer (mCRPC) and the PK of BAY 1841788 and its major metabolite BAY 1896953.

The drug product is licensed from Orion pharma, Finland which is also the manufacturer of the product.

Inclusion Criteria:

• Japanese males aged ≥ 20 years

• Histologically or cytologically confirmed adenocarcinoma of prostate without neuroendocrine differentiation or small cell features

• Patients with metastatic castration-resistant prostate cancer (mCRPC). CRPC is defined as follows

  • Ongoing androgen deprivation therapy with a luteinizing hormone-releasing hormone (LHRH) analogue or antagonist, or bilateral orchiectomy, and castrate level of serum testosterone (< 1.7 nmol/l [50 ng/dL]) at screening AND
  • Progressive disease and/or prostate-specific antigen (PSA) increase of three consecutive rises, at least 1 week apart AND
  • PSA > 2ng/mL at screening

• Eastern Cooperative Oncology Group performance status (ECOG PS) of 0-1

• Life expectancy of at least 3 months

• Blood counts at screening: haemoglobin ≥ 9.0 g/dL, absolute neutrophil count ≥ 1,500/μL (1.5x109/l), platelet count ≥ 100,000/μL (100x109/l) (patient must not have received any growth factor or blood transfusion within 7 days of the hematology laboratory obtained at screening)

• Screening values of serum alanine aminotransferase (ALT) and/or aspartate transaminase (AST) ≤ 2.5 x upper limit of normal (ULN), total bilirubin ≤ 1.5 x ULN, creatinine ≤ 1.5 x ULN, albumin > 3.0 g/dl

• Prior treatment with antiandrogen. Discontinuation of bicalutamide or nilutamide (not approved in Japan) at least 6 weeks and other antiandrogens at least 4 weeks prior to the start of the study drug administration.

Exclusion Criteria:

• Known metastases in the brain
• Symptomatic local-regional disease that requires medical intervention including moderate/severe urinary obstruction or hydronephrosis due to prostate cancer
• Acute toxicities (except for alopecia and CTCAE grade 2 neuropathy) of prior treatments and procedures not resolved to CTCAE ≤ grade 1 or baseline before the first drug administration
• Febrile neutropenia of Common Terminology Criteria for Adverse Events (CTCAE) ≥ 3
• History of other malignancy within the previous 5 years except a basal cell carcinoma of skin and any other cancer for which treatment has been completed ≥ 5 years ago and from which the patient has been disease-free5 years ago and from which the patient has been disease-free
• Prior treatment within 4 weeks before the first drug administration with immunotherapy, antiandrogen, CYP17 inhibitor (CYP17i), oral ketoconazole, estrogens, 5-α reductase inhibitors or investigational treatment
• Use of bicalutamide or nilutamide (not approved in Japan) within 6 weeks before the first drug administration
• Radiation therapy (external beam radiation therapy [EBRT], brachytherapy, or radiopharmaceuticals) or chemotherapy (except for nitrosoureas and mitomycin C) within 4 weeks before the first drug administration. Use of nitrosoureas or mitomycin C within 6 weeks before the first drug administration.
• Prior use of any herbal products known to decrease PSA levels (e.g. PC SPES or saw palmetto) within 4 weeks before the first drug administration