The accumulation of tumor-cell-derived acetic acids exacerbates the immune suppression of FFAR2-expressing MDSCs through up-regulation of Arg1 expression and L-Arginine consumption in tumor microenvironment, which contribute to immune suppression and cancer progression in a Gαq/Calcium/ PPAR-γ/Arg1 signaling dependent manner. Here, FFAR2 is linked to cancer.