As generally happens with PTs, V-ATPase proton pumps (PPs) are highly expressed in many tumors, apart from in BC, following the same rule of PTs, namely that their upregulation is a sign of bad prognosis, facilitating faster cancer growth, tissue invasion, the metastatic process and chemotherapy resistance (MDR), either in BC or other malignant tumors [96,97,98]. The gene discussed is PTS; the disease is cancer.