RecruitingEarly Phase 1Diagnostic testBreast Cancer PSMA PETThe purpose of this research is to determine the expression of Prostate Specific Membrane Antigen(PSMA) in metastatic Triple Negative Breast Cancer (TNBC) patients using Fludeoxyglucose F18 (FDG) PET/CT as the gold standard. The investigators hypothesize that most lesions in metastatic TNBC are PSMA-avid; and thus PSMA-based radionuclide therapy can be a valid treatment option for TNBC, and clinical trials can be designed for this purpose. Thirty metastatic TNBC patients will be enrolled and will be on the study for maximum of 4 weeks.