Is it Time to Include p40 as a Standard Myoepithelial Marker of Breast? A Comparative Study of Expression of p63 and p40 in Benign Breast Diseases and Invasive Ductal Carcinomas of the Breast

Context: The expression of p40 in breast tissue as a myoepithelial marker is not extensively studied. This study was designed to find the expression of two markers p63 and p40 in benign breast diseases and Invasive ductal carcinomas (IDCs) of the breast. Aim: A series of cases of fibroadenoma and IDC of breast were studied for expression of p40 and compared to the p63 staining profile. Settings and Design: A total of 118 cases of breast disease were selected for this study from the archives of a tertiary care hospital, which included 41 cases of benign and 77 cases of malignant etiology. After the exclusion, 30 cases of fibroadenoma and 68 cases of IDC, were selected for the study. Subjects and Methods: Samples (n = 98) included fibroadenoma (n = 30) and IDC (n = 68). IDC was studied as a whole group and was also divided as triple negative breast cancer (TNBCs, n = 12) and Non-Triple TNBCs (NTNBC, n = 56). The expression of p63 and p40 was assessed in myoepithelial cells (MECs) in fibroadenoma and tumor cells in IDC. Results: Both the antibodies performed similarly to highlight MECs in fibroadenoma in all 30 cases. In IDC, TNBC and NTNBC subgroups p63 stained the tumor cells more than p40. None of the tumor cells in the NTNBC group exhibited positivity for p40. Conclusions: As a MEC marker, both p63 and p40 perform similarly but in IDC (TNBC and NTNBC), the tumor cells of IDC stain significantly more for p63 than p40. It appears that p40 does not come positive in the tumor cells of NTNBC.