PSMA ADC 2301EXT is an open-label study to further assess the anti-tumor activity as measured by radiographic imaging and biomarkers, safety and tolerability of Prostate Specific Membrane Antigen Antibody Drug Conjugate (PSMA ADC) in subjects with mCRPC. Subjects who have participated in the PSMA ADC 2301 study and who, in the opinion of the Principal Investigator are likely to benefit from continued treatment with PSMA ADC are eligible for the PSMA ADC 2301 extension study. Subjects who are benefiting from treatment may be able to receive up to an additional eight to sixteen doses (every 3 weeks) of PSMA ADC.