Radiologically Guided Biopsies of mCRPC

Inclusion Criteria: * History of histologically confirmed prostate cancer. Patients without histologically confirmed prostate cancer are eligible if both the treating physician and the study investigator agree that the patient's history is unambiguously indicative of advanced prostate cancer (e.g. high PSA responsive to Androgen Deprivation Therapy.) * Radiographic evidence of metastatic disease amenable to image-guided biopsy of a metastatic site. Soft-tissue as well as bony metastatic lesions will be considered acceptable. Patients with locally advanced disease only (where the biopsy would be of a prostatic mass) are not eligible. Biopsy of newly emerging radiographic metastases is desired and preferable to the biopsy of previously existing lesions whenever possible. * Platelets \>75,000/μl within 14 days prior to biopsy * Prothrombin time (PT) or International Normalized Ratio (INR) and a partial thromboplastin time (PTT) \< 1.5 times the institutional upper limit of normal (ULN) within 14 days prior to biopsy. * Patients on warfarin, aspirin, or other anti-coagulants are eligible provided they are deemed able to tolerate discontinuation of anti-coagulation for one week prior to the biopsy. Conversion to low molecular weight heparin prior to biopsy is permitted per local standard operating procedures, provided there is agreement regarding the procedure between the treating physician, the interventional radiologist and the PI. * Castrate levels of testosterone (testosterone \<50n g/dL) within 28 days prior to biopsy. * Patients with significant congenital or acquired bleeding disorders (eg von Wildebrand's disease, acquired bleeding factor inhibitors) are not eligible. * If no prior orchiectomy, medical castration therapy must continue while on study. * Prostate-specific antigen (PSA) level obtained within 28 days prior to biopsy. * Patients currently on first generation oral anti-androgens (flutamide, bicalutamide, nilutamide) must have progressed after at least 4 weeks of anti-androgen discontinuation. * Patient's disease is currently progressing (in setting of testosterone \< 50 ng/dl), defined by any of the following criteria: * PSA Progression: PSA level of at least 2 ng/ml which has risen on at least 2 successive occasions, at least one week apart. If the confirmatory PSA (#3) value is less (i.e., #3b) than the screening PSA (#2) value, then an additional test for rising PSA (#4) will be required to document progression for the purposes of eligibility. * Soft tissue progression: by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 * Bone scan progression: the appearance of \>=2 new lesions. Symptomatic progression in an area of radiologically evident disease. * One of the following criteria must be met: * Evidence of disease progression (as defined above) following treatment with at least 2 months of abiraterone acetate, enzalutamide, or ARN509 - based therapy. * Enrollment on a high priority clinical trial conducted by the West Coast Dream Team (WCDT). Examples include trials with biopsy obtained before abiraterone or enzalutamide therapy, and following development of resistance to those agent(s). This list is maintained by the lead site. * Evidence of disease progression (as defined above) in patients with "aggressive phenotype" metastatic castration resistant prostate cancer (mCRPC) with at least one of the following clinical features * Visceral or brain metastases * Known small cell or neuro-endocrine subtypes (by Immunohistochemistry (IHC) or serum markers) * Primary androgen deprivation therapy (ADT) resistance defined as a nadir PSA of \> 4 ng/dl after 7 months of primary androgen deprivation (with Testosterone \< 50 ng/dl.) * Prior chemotherapy for Castration Resistant Prostate Cancer is not allowed * Age \> 18 years * Eastern Cooperative Oncology Group (ECOG) Performance status 0-3 * Ability to understand and the willingness to sign a written informed consent document