The lack of Upase would lead to the accumulation of uridine that has been reported a crucial function to reduce 5‐FU toxicity in normal tissues.9 BAU, an inhibitor of UPase, is able to protect normal tissues from 5‐Fu host toxicity.24, 25, 26 Also, Upase was discovered to be a higher enzymatic activity in most human tumours. This evidence concerns the gene UPP1 and neoplasm.