CTSD and breast cancer: Kim et al. used the SILAC method to investigate the proteomic profiles of MDA-MB-231 BC cells treated with single or fractionated RT and found several tumor-associated factors, such as cathepsin D (CTSD), gelsolin (GSN), and mannose receptor C type 2 (MRC2), upregulated after irradiation and in a dose-dependent manner [150].