VEGFA and cancer: This leads to the aggravation of colitis and the occurrence of colon cancer.[172] In addition, TMAO induces the secretion of VEGFA from tumors and promotes the angiogenesis and the proliferation of HCT116 cells.[173] However, TMAO activates the immune system and has shown to be of great benefit in cancer immunotherapy.[159, 166] Niacin is an important vitamin produced by gut microbes.