As Warburg effect has long been demonstrated since several decades ago, cancer cells tend to show aerobic glyclysis to produce lactate. In addition, xCT transporter, which releases glutamate and uptakes cysteine for the glutathione (GSH) synthesis, also contributes to the formation of acidic microenvironment. These are the main reasons that tumor microenvironment is relatively acidic and that the adaptation to low pH conditions is beneficial for the survival and growth of tumor cells.