Low ratio of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol-glucuronides (NNAL-Gluc)/free NNAL increases urothelial carcinoma risk

► People with higher cumulative cigarette smoking exposure had higher NNK metabolites. ► Decreased NNAL-Gluc/free NNAL ratio related to a significantly increased UC risk. ► Cigarette smoking exposure interacted significantly with low NNAL-Gluc/free NNAL to UC.