ARCTIC: Liquid Biomarkers in the Prospective Androgen Receptor Signaling Inhibitors (ARSI) Resistance Clinical Trials

This study will follow men with metastatic castration resistant prostate cancer throughout their standard of care treatment for their disease to determine if the presence of different genes or proteins can predict which patients respond to the cancer treatment they receive. As tumors grow and begin to spread, they may release cells into patients' bloodstream. These cells are called "circulating tumor cells", or CTCs. CTCs can be used to look for differences in "biomarkers" (genes or proteins that may change based on how a person is or is not responding to treatment). The purpose of this research study is to learn whether scientists can use biomarkers from CTCs to predict which tumors will respond to certain hormonal therapies. Participants will have blood collected and provide an archival sample from a previous tumor biopsy. The researchers will compare biomarkers from participants who responded well to treatment to those who responded poorly in order to answer the research question.