CD81 and neoplasm: Thus, using MCF7, BT474, SK-BR-3, and MDA-MB-231 BC cell lines, specific tumor biomarkers of exosomes have been detected by Wang et al. (2023), such as prostate specific membrane antigen (PSMA), EGFR, cluster of differentiation 81/tetraspanin 1 (CD81/TAPA-1), and carcinoembryonic antigen (CEA) (Wang et al., 2023).