SIRT5 and cholangiocarcinoma: Abnormal and ectopic CPS1 expression in tumour cells may lead to urea cycle deficiency and a nucleic acid pool imbalance.15, 16, 29 CPS1 overexpression is associated with poor prognosis in several types of cancer, such as colon cancer, cholangiocarcinoma and glioblastoma.30, 31, 32 CPS1 has also been reported to be regulated by hepatocyte nuclear factor 3β (HNF3β) and sirtuin 5 (SIRT5) by their transcriptional activation or deacetylation‐ and deglutarylation‐mediated activation.33, 34, 35 Thus, the results of our study might supplement the previous reported associations.