5‐fluorouracil (5‐FU) has been widely used to be a chemotherapeutic agent in the treatment of various cancers across the world.27, 28 However, 5‐FU–based therapeutic has limited clinical treatment because of dose‐limiting cytotoxicity.29 BAU, an inhibitor of UPase, has been reported could reduce 5‐FU toxicity. The gene discussed is UPP1; the disease is cancer.