In colon cancer, the dysregulation of gut microbiota is accompanied by the release of endotoxin lipopolysaccharide (LPS) and cathepsin K. Cathepsin K binds toll-like receptor 4 (TLR4) on macrophages surfaces to activate the mTOR pathway, enhancing the M2 polarization of tumor-associated macrophages and promoting cancer progression via the mTOR-dependent pathway [117,118]. Here, CTSK is linked to cancer.