Previous studies have demonstrated the key role of different types of cathepsins in cancer cell invasion, such as cathepsin (CTS) B in glioma (Demchik et al., 1999), CTS-L in ovarian carcinoma (Zhang et al., 2014), and CTS-S in colorectal (Burden et al., 2009) and breast cancer metastasis (Sevenich et al., 2014). This evidence concerns the gene CTSS and breast cancer.