Although CTSD, an aspartyl protease, is overexpressed and secreted by breast carcinomas, we demonstrated that cysteine proteases (CTSB, CTSK, CTSL, and CTSS) rather than the aspartyl proteases participated in TNBC invasion through blocking or inhibiting them individually via siRNA transfection and specific inhibitors. This evidence concerns the gene CTSK and breast carcinoma.