Immunohistochemical studies have shown that ErbB3 is expressed or overexpressed in greater than 50% of DCIS and invasive breast cancers (Gasparini et al, 1994; Bobrow et al, 1997; Naidu et al, 1998) and correlates with poor prognosis (Rajkumar et al, 1996; Lee et al, 2002; Bieche et al, 2003; Witton et al, 2003; Tovey et al, 2004). Here, ERBB3 is linked to ductal breast carcinoma in situ.