Prostate-specific Membrane Antigen Antibody-Drug Conjugate (PSMA ADC) 1301EXT is an open-label, nonrandomized, phase 1 extension study of PSMA ADC administered IV in subjects with progressive CMPC that has progressed after prior taxane therapy. Subjects who have participated in PSMA ADC 1301 and who, in the opinion of the PI, are likely to benefit from continued treatment with PSMA ADC will be enrolled in PSMA ADC 1301EXT.

Inclusion Criteria:

1. Subjects who have completed the PSMA ADC 1301 study and who, in the opinion of the investigator, have derived benefit from treatment with PSMA ADC.
2. A diagnosis of progressive, castration-resistant, metastatic prostate cancer.
3. Prior chemotherapy regimens, one of which contains taxane.
4. Eastern Cooperative Oncology Group status of 0 or 1

Exclusion Criteria:

1. Clinically significant cardiac disease or severe debilitation pulmonary disease
2. Evidence of an active infection requiring ongoing antibiotic therapy
3. History of drug and/or alcohol abuse