ATP6AP1 and malignant colon neoplasm: In addition, we found V-ATPase related genes including ATP6V1A, ATP6V0D1, ATP6AP1 and ATP6AP2 expression were positively correlated with M2 macrophage infiltration but not M1 macrophage in TCGA colon cancer and breast cancer dataset (Figures 5M, N and Figures S4G–S4L), which is consistent with our findings that acidic tumor microenvironment facilitated polarization and recruitment of M2-like macrophages.