This is an open-label, multicenter Phase 1 study of DEC003M, in patients with advanced stage prostate cancer. The study consists of a dose-escalation phase to determine the dose for expansion, followed by a dose-expansion phase to evaluate preliminary antitumor activity, safety, and pharmacokinetics.

Inclusion Criteria:

1. At the time of informed consent, be ≥18 years of age.
2. Histologically confirmed adenocarcinoma of the prostate.
3. Metastatic castration-resistant prostate cancer (mCRPC) with documented disease progression despite androgen deprivation therapy.
4. Prior orchiectomy or medical castration, or continuous treatment with luteinizing hormone releasing hormone analogues (LHRHa) .
5. Measurable disease prior to enrollment.
6. Testosterone at castration level.
7. Progressed on standard therapy, or intolerant to standard therapy, or ineligible for standard therapy, or no standard therapy available.
8. At least 1 prior Androgen Receptor Pathway Inhibitor.
9. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

Exclusion Criteria:

1. History of other malignancies.
2. Inadequate organ function.
3. Active autoimmune disease.
4. Active CNS involvement.
5. Uncontrolled or clinically significant cardiovascular and cerebrovascular diseases.
6. Any prior medical history of ILD/pneumonitis.
7. Clinically significant corneal disorder or known severe dry eye.
8. Grade 2 or higher peripheral neuropathy.
9. Inadequate washout period for prior anticancer treatment.
10. Any known history of or suspicion for history of clinically significant liver disease .
11. Known hypersensitivity to any component of the DEC003M.
12. Prior treatment with a PSMA-targeted antibody therapy.
13. Other conditions judged by the investigator that may have effects on the patient's participation in the study.