Mucinous lesions of the breast. A pathological continuum.

Mucocele-like tumor and invasive mucinous carcinoma of the breast may represent the two ends of the pathological spectrum of mucinous lesions of the breast, respectively. Little data exists on mucinous lesions that may be considered intermediate between mucocele-like tumor and invasive mucinous carcinoma. We studied 23 consecutive cases of invasive mucinous carcinoma of the breast and observed the following associated intermediate mucinous lesions: mucin-filled ducts (MFD) with unremarkable epithelium in 15 cases (65%), MFD with typical ductal hyperplasia in 9 cases (39%), MFD with atypical ductal hyperplasia in 5 cases (22%), and MFD with intraductal carcinoma in 13 cases (57%; micropapillary or cribriform types). Eighteen cases (78%) contained MFD with one of these four lesions and five cases (22%) contained all four lesions. Twenty-three consecutive cases of infiltrating ductal carcinoma-not otherwise specified (IDC-NOS), 21 cases of intraductal carcinoma, and 50 consecutive cases of surgically-excised breast tissue with fibrocystic change (FC), were similarly reviewed. Only one case (4%) of IDC-NOS, 1 case of intraductal carcinoma, and two cases (4%) of FC, contained small foci of MFD with intraductal carcinoma, intraductal carcinoma, and unremarkable epithelium, respectively. Our findings suggest the presence of a spectrum of mucinous lesions of the breast which represents a pathological continuum.