ASIC1 and neoplasm: Finally, while NHE1 upregulation and its extracellular consequences (low pHe and CPR) indicate that H+ is the fundamental mechanism behind fast pHi-driven tumor growth and metastatic progression, similar pH changes can also be mediated by other membrane-bound proton transporters (PTs), such as monocarboxylate transporters (MCTs), acid-sensing ion channel type 1 (ASIC1), and proton pumps (PPs) [44,82,83,84,85,86,87,88,89] (Figure 1).