Different panels of markers should be used to predict mammary Paget's disease associated with in situ or invasive ductal carcinoma of the breast.

Mammary Paget's disease (MPD) is a rare manifestation of breast carcinoma involving the nipple. Our objective was to identify molecular markers and molecular subtypes that may predict patients at high risk of developing MPD. Immunohistochemical (IHC) analyses were performed with antibodies to estrogen receptor (ER), progesterone receptor (PR), androgen receptor (AR), HER2, epidermal growth factor receptor (EGFR), and several cytokeratins (CK5/6, CK14, CK17, CK8, CK18) on representative sections of 121 cases of ductal carcinoma of the breast, including 28 cases with MPD, 81 cases with neither MPD nor nipple involvement, and 12 cases of non-MPD with nipple involvement. The rates of receptor expression and subtype distributions of 3 IHC-based molecular classifications were compared among these groups. The results showed that: (1) MPD is more likely to be associated with ER- and PR-negative ductal carcinoma in situ (DCIS), but not invasive ductal carcinoma (IDC); (2) MPD is more likely to be associated with HER2-over expression subtype DCIS, but not IDC; and (3) carcinomas with non-MPD nipple involvement differ from those with MPD, since they are more likely to be ER- and PR-positive, HER2-negative, and luminal A subtype. In summary, different panels of markers should be used to predict MPD associated with different underlying lesions; for DCIS, the ER-negative, PR-negative, and HER2-subtype and not basal-like subtype is most predictive of MPD; for IDC, the luminal B-subtype is most predictive of MPD.