RecruitingA Study for CTC Expression and cfDNA/RNA Assessment in Metastatic Breast Cancer PatientsThe purpose of this research is to learn if the CellSearch Circulating Tumor Cells (CTC) test can help doctors in making decisions about treatment and monitoring of breast cancer. The test consists of diagnostic CTC counts (enumeration) and expression of biomarkers Human Epidermal growth factor Receptor 2 (HER2), Estrogen Receptor (ER), and programmed death-ligand 1 (PD-L1) and cell free DNA/RNA (cfDNA/RNA) analysis.