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Recently , the differential gene expression response in wild - type and cancer - prone Xpa ( - / - ) p53 ( + / - ) primary mouse hepatocytes after exposure to benzo [ a ] pyrene ( B [ a ] P ) revealed downregulation of cancer - related pathways in Xpa ( - / - ) p53 ( + / - ) hepatocytes only .
 Chemical: benzo [ a ] pyrene; Chemical: B [ a ] P
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: benzo [ a ] pyrene; Chemical: B [ a ] P