Inclusion Criteria:  Participants must have histologically or cytologically confirmed adenocarcinoma of the prostate. Patients with neuroendocrine component are eligible. Participants must have castrate levels of serum testosterone < 50 ng/dL. Participants without orchiectomy must be maintained on luteinizing hormone releasing hormone (LHRH) agonist/antagonist. Participants must have received prior abiraterone and/or next generation androgen receptor antagonist (enzalutamide, apalutamide, or darolutamide) for hormone sensitive disease or CRPC. Prior docetaxel for hormone sensitive disease is permitted. Participants must have progressive disease. Patients with non-measurable disease are eligible. Eastern Cooperative Oncology Group performance status ≤1 (Karnofsky ≥80%). Patients must have normal organ and marrow function.  Exclusion Criteria:  No pure small cell carcinoma. Prior treatment with cirmtuzumab. No prior treatment with docetaxel for CRPC. Treatment with abiraterone, apalutamide, or darolutamide within 2 weeks of treatment initiation. Treatment with cytotoxic chemotherapy within 3 weeks of treatment initiation. Treatment enzalutamide or other investigational prostate cancer directed therapy within 4 weeks of treatment initiation. Palliative radiation therapy to the bone or other sites within 2 weeks of treatment initiation. Imminent or established spinal cord compression based on clinical and/or imaging findings. Known active central nervous system metastases and/or carcinomatous meningitis. Uncontrolled intercurrent illness or clinically significant medical condition. Treatment with antimicrobial agent within 4 weeks of treatment initiation.