Immunohistochemistry of mammary Paget's disease. Cytokeratin 7, GATA3, and HER2 are sensitive markers

To investigate the expression of various immunohistochemical markers in Mammary Paget's disease (MPD) and MPD-associated breast carcinoma and to evaluate their value in establishing the diagnosis. This retrospective descriptive study was carried out at King Faisal Specialist Hospital and Research Center and King Khalid University Hospital, Riyadh, Saudi Arabia. All MPD cases reported between January 2010 and June 2016 were selected from the surgical pathology records. Immunohistochemical staining was carried out for cytokeratin 7 (CK7), GATA-binding protein 3 (GATA3), human epidermal growth factor receptor 2 (HER2), and estrogen, and progesterone receptors. Results: Twenty-two cases of MPD and 20 cases of MPD-associated breast carcinoma were included. CK7 was positive in 95% (21/22) cases of MPD and in all (20/20) cases of associated breast carcinoma. Similarly, GATA3 was expressed in 95% cases of both MPD (21/22) and associated breast carcinoma (19/20). Human epidermal growth factor receptor 2 was also overexpressed in 90% cases of MPD (20/22) and associated breast carcinoma (18/20). Estrogen stained positive in 27% cases of MPD (6/22) and 30% of cases of associated breast carcinoma (6/20). Progesterone receptors was not positive in any case of MPD; however, it was seen positive in 25% cases of MPD-associated breast carcinoma (5/20). CK7, GATA3, and HER2 are widely expressed in MPD and MPD-associated breast carcinoma. These markers can be used for the immunohistochemical confirmation of MPD including CK7-negative cases.