Mechanisms of Resistance to PSMA Radioligand Therapy

Inclusion Criteria: 1. Initiating treatment with Lutetium based PSMA-targeted RLT. 2. Participants must have a PSMA-avid lesion that is accessible to biopsy. Biopsy of newly emerging radiographic metastases is desired and preferable to the biopsy of previously existing lesions whenever possible. Newly emerging lesions are defined as those that are absent on a previous scan, or those demonstrating unequivocal progression since initiation of the last treatment. Biopsies will be performed according to local institutional standards. 3. Patients on warfarin, aspirin, or other anti-coagulants are eligible provided they are deemed able to tolerate discontinuation of anti-coagulation for at least five days prior to the biopsy. Conversion to low molecular weight heparin prior to biopsy is permitted per local standard operating procedures, provided there is approval by the interventional radiologist or the PI. 4. Age \>=18 years. 5. Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: 1. Patients with significant congenital or acquired bleeding disorders (eg von Wildebrand's disease, acquired bleeding factor inhibitors). 2. Patients who are not able to undergo additional study related imaging procedures.