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In this study , we report the development of a knock - in mouse model for breast cancer where the endogenous Pik3ca allele was modified to allow tissue - specific conditional expression of a frequently found Pik3ca ( H1047R ) ( Pik3ca ( e20H1047R ) ) mutant allele .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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