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Recent breast cancer clinical trials have examined whether combinations of drugs targeting transmembrane receptors or their downstream effectors involved in cell signal transduction can increase response rates and overcome acquired and / or de novo drug resistance compared to a single targeted agent with or without systemic chemotherapy .
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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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