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Recently, the development of monoclonal antibodies directed against ER has been applied to the study of breast carcinomas and results obtained show good correlation with the quantitative SBA .
 protein: ER
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 protein: ER