p40 (ΔNp63) expression in breast disease and its correlation with p63 immunohistochemistry

p63 protein is widely used to identify myoepithelial cells in breast disease. There have been no comparative studies of the p63 antibodies which detect different isoforms. In this study, we examine the expression profiles of p63 protein in benign proliferative diseases and malignant tumors of the breast using pan-p63 and p40 antibodies, and analyze their diagnostic utility and clinical implications. We selected 32 adenoses, 34 intraductal papillomas, 31 ductal carcinoma in situ (DCIS), 257 invasive ductal carcinoma (IDC), and 36 metaplastic carcinomas, and created tissue microarray blocks from them. Immunohistochemical assays for p63 protein were performed on these samples. We investigated the expression patterns of the pan-p63 (TP63, 4A4, Dako, 1:700), p40 antibody [5-17, CalBiochem/EMD Biosciences, 1:2000, p40 (CB)], and p40 antibody [polyclonal, Diagnostic BioSystems, 1:100, p40 (DB)] in various forms of breast disease. We determined that p63 and p40 (DB) expression in myoepithelial cells was broadly similar and showed cognate clinicopathologic features, unlike p40 (CB). p40 (CB) was more sensitive (99.0%) but less specific (85.8%), and p63 was less sensitive (93.8%) in adenosis, IP, and DCIS. In IDCs, p63 and p40 (DB) had similar expression in cancer cells; p40 (CB) expression, however, was statistically different. In metaplastic carcinomas, both p63 and p40 (DB) had distinct expression profiles, according to their histologic subtypes. We conclude that p40 antibodies as well as pan-p63 antibody are specific and sensitive myoepithelial cell markers. Interpretation of p40 positivity in cancer cells, however, should be considered carefully, due to their relatively lower specificity.