4672
Therefore , our study aimed to evaluate the roles of two gene polymorphisms ( CYP2A13 and UGT2B7 ) of NNK metabolism - related enzymes in the carcinogenesis of UC in Taiwan .
 Chemical: NNK
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: NNK