Abstract: Objective 　To study the significance of fascin protein expression in ductal intraepithelial neoplasia (DIN) and invasive ductal carcinoma (IDC).Methods Thirty cases of usual ductal hyperplasia (UDH) , 30 cases of flat epithelial atypia (FEA，DIN1a) , 15 cases of atypical ductal hyperplasia (ADH，DIN1b) ， 2 cases of DCIS grade1（DIN1c），10 cases of DCIS grade2（DIN2）and 18 cases of DCIS grade3（DIN3）were immunohistochemically investigated using monoclonal antifascin antibody and compared with 120 cases of invasive ductal carcinoma (IDC). Results Fascin protein expression was not seen in normal breast tissue， UDH， FEA (DIN1a) ， ADH(DIN1b)，DCIS grade1（DIN1c）and DCIS grade2（DIN2）, and was only seen in 2 out of 18 cases of DCIS grade3（DIN3）(11.1%), and 18 out of 120 cases of IDC (15%) . Fascin protein expression was correlated with ER negative（P＜0.05）、 PR negative（P＜0.05）、 tumor grade（P＜0.05）and axillary lymph node status（P＜0.05）, but not correlated with age、location、tumor sizeand HER2 expression.Conclusions Fascin protein expression seems to be a late event, usually present in carcinoma. Targetting the fascin pathway may be a noval therapeutic strategy of mammary carcinoma.

Key words: Ductal intraepithelial neoplasia , UDH, FEA, ADH, DCIS, IDC, Fascin