CD44 and breast cancer: As shown in Figure 1, examples of BC biomarkers include protein biomarkers such as human epidermal growth factor receptor 2 (HER2), Carcinoembryonic Antigen (CEA), Cancer antigen 15-3 (CA15-3), Mucin 1 (MUC1), cell biomarkers such as Michigan cancer foundation-7 (MCF-7), MDA-MB-231, DNA/genetic biomarkers such as microRNA-155 (miRNA-155), microRNA 21 (miRNA-21), breast cancer 1 (BRCA1), breast cancer 2 (BRCA2), cluster of differentiation 24 (CD-24), cluster of differentiation 44 (CD-44), and other metabolites such as H2O2 [49,50,51,52].