CTSD and breast cancer: The proteomic comparisons notably led to the identification of five proteins that are used as breast cancer diagnostic and prognostic biomarkers: proliferating cell nuclear antigen (PCNA), cathepsin D, cathepsin B, protein S100-A14, and heat shock protein beta-1 (HSP27) [9], [10], [14], [15] (Table 1 and 2).