11320
Given the important role of the estrogen receptor ( ER ) in the development and physiology of the breast , it is essential to delineate the mechanisms responsible for its failed expression in some breast tumors .
 ( protein: estrogen receptor, None) , ( protein: ER, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( protein: estrogen receptor, None) , ( protein: ER, None) 