HCAR2 and breast cancer: In addition, GPR109A deficiency leads to early development and metastasis of breast cancer.138 Moreover, the knockdown of GPR109A leads to increased proliferation of breast cancer cells and GPR109A activation inhibits tumor growth.115,138,139 This phenomenon can be explained by the lack of dietary fiber/SCFAs which leads to the development, differentiation or accumulation of inflammatory immune cells in the intestine and local lymph nodes.