CTSS and cancer: In the advanced stages of tumor development, M2-like TAMs facilitate the invasive behavior of cancer cell and metastatic progression through the release of various proteases involved in ECM digestion (i.e., members of the MMP and cathepsin families) [53], promoting the evasion of tumor-initiating cells, by expressing mediators of both cancer cell stemness (i.e., IL-6, PDGF, IL-1) [54] and proliferation (i.e., epidermal growth factor/EGF), and facilitating the epithelial-mesenchymal transition (EMT) [55].