ProstACT: This study is investigating a PSMA-targeted antibody when given in addition to standard of care, compared to standard of care alone, in people with metastatic castration-resistant prostate cancer (mCRPC) that expresses PSMA and has progressed on prior treatment with a novel androgen axis drug (NAAD)A Multinational, Multicenter, Prospective, Randomized, Controlled, Open Label Phase 3 Study With Best Standard of Care With and Without 177Lu-DOTA-rosopatamab for Patients With PSMA Expressing Metastatic Castration-resistant Prostate Cancer Progressing Despite Prior Treatment With a Novel Androgen Axis Drug

Inclusion

1. Be a male, at least 18 years old, with metastatic adenocarcinoma of the prostate defined by histological / pathological confirmation of PC.
2. Be of ECOG Performance Status 0, 1, or 2 and have an estimated life expectancy of ≥6 months.
3. Have metastatic disease (≥1 metastatic lesions present on baseline CT, MRI, or bone scan imaging).
4. Have castration-resistant PC (defined as disease progressing despite castration by orchiectomy or ongoing use of luteinizing hormone-releasing hormone [LHRH]) and must have a castrate level of serum/plasma testosterone (<50 ng/dL or <1.7 nmol/L).
5. In the mCRPC setting, must have received a minimum of 12 weeks of prior therapy with a NAAD, either enzalutamide or abiraterone plus prednisone.
6. Should have received one line of prior taxane therapy or have refused or be ineligible for taxanes

7. Have a disease that is progressing at study entry, despite a castrate testosterone level (<50 ng/dL or <1.7 nmol/L), by the demonstration of at least one of the following:

   1. Rising PSA values done in sequence at least 1 week apart and with a minimal starting value of 2.0 ng/mL.
   2. Progressive disease or new lesion(s) in the viscera or lymph nodes as per RECIST1.1 or in bone as per Prostate Cancer Working Group 3 [PCWG3; Scher et al., 2016]). Any ambiguous results are to be confirmed by other imaging modality (e.g., CT or MRI scan).
8. Have disease that is PSMA positive, as demonstrated by a 68Ga-PSMA11 PET/CT scan and confirmed as eligible by the Sponsor's central reader (patient must have at least one site of metastatic disease with SUVmax ≥1.5 times the SUV of normal liver). If the disease meets the criteria for PSMA positivity, but there is one or more soft tissue lesion of ≥ 2 cm that is not PSMA positive, then the patient is to be excluded on the grounds that there is substantial disease which might not respond to the therapy.
9. Must have recovered to ≤ Grade 2 from all clinically significant toxicities related to prior therapies (i.e., surgery, local radiotherapy, NAAD, chemotherapy, etc.).
10. Can be receiving a bisphosphonate or denosumab regimen provided that the patient has been receiving and tolerating this treatment for ≥30 days prior to randomization.

11. Have adequate organ function at Screening:

    a. Bone marrow: i. Platelets ≥150×109/L. ii. Absolute neutrophil count >1.5×109/L. iii. Hemoglobin ≥10g/dL (no red blood cell transfusion in the previous 4 weeks).

    b. Liver function: i. Total bilirubin < 1.5×the upper limit of normal (ULN). For patients with known Gilbert's Syndrome <3×ULN is permitted. ii. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) <3×ULN OR <5×ULN for patients with liver metastases. c. Renal function: i. Serum/plasma creatinine <1.5×ULN or creatinine clearance ≥50 mL/min determined using the Cockcroft & Gault formula.

12. Have the capacity to understand the study and be able and willing to comply with all protocol requirements.
13. Patients must comply with the radiation protection rules (including hospital admissions and isolation) that are used by the treating institution in order to protect their contacts and the general public, especially if a female partner of the patient is or could be pregnant.
14. Must agree to practice adequate precautions to prevent pregnancy in a partner and to avoid potential problems associated with radiation exposure to the unborn child (Refer to Clinical Trials Facilitation Group, 2020: Recommendations related to contraception and pregnancy testing in clinical trials Version 1.1, CTFG, 2020).