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A recent phase II trial reported a statistically significant improvement in PFS with the addition of an oral inhibitor of cyclin - dependent kinase 4 / 6 to letrozole compared to letrozole alone ( 26 . 1 versus 7 . 5 months ) .
 Chemical: letrozole; Chemical: letrozole
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: letrozole; Chemical: letrozole