Research ArticlesImmunohistochemical Expression of Microfibrillar-associated Protein 5 (MFAP5) in Invasive Breast Carcinoma of No Special TypeDawoud, Marwa M. MD*; Abouelfadl, Dalia MD†; Abdou, Asmaa G. MD*; Elkhouly, Enas A.B. MD‡Author Information Departments of *Pathology ‡Oncology, Faculty of Medicine, Menoufia University †Department of Pathology, Medical Research Division, National Research Center, Egypt The authors declare no conflict of interest. Reprints: Asmaa G. Abdou, MD, Department of Pathology, Faculty of Medicine, Menoufia University, Shebein Elkom 32511, Egypt (e-mail: [email protected]). Applied Immunohistochemistry & Molecular Morphology: October 2019 - Volume 27 - Issue 9 - p 649-657 doi: 10.1097/PAI.0000000000000686 Buy Metrics Abstract Breast cancer (BC) remains the most prevalent female cancer in Egypt and worldwide. Microfibrillar-associated protein 5 (MFAP5) is a multifunctional glycoprotein. Although MFAP5 gene was among the genes that found globally expressed in human cancers, it had been only recently reported in few cancer research studies. This is a retrospective study that has been conducted on 66 Egyptian patients who had invasive carcinoma of no special type. Immunohistochemical staining for MFAP5 was applied on the archival formalin-fixed paraffin-embedded blocks. Staining was assessed semiquantitatively and correlated with the available clinicopathologic parameters and immunohistochemical subtypes of BC. MFAP5 epithelial cytoplasmic expression was observed in 89.4% (59/66) of cases. In contrast, nuclear expression was seen in non-neoplastic breast lobules and premalignant lesions adjacent to tumors that also exhibited constant staining in myoepithelial layer. Statistical analysis of epithelial cytoplasmic expression revealed association of MFAP5 expression with tumor size (P=0.046), high histologic grade (P=0.007), presence of lymph node metastasis (P=0.014), poor Nottingham Prognostic Index (NPI) (P=0.001), late stage (P=0.008), immunohistochemical subtypes of BC (P=0.018), and increased microvessel density using CD34 immunostianing (P=0.04). MFAP5 cytoplasmic expression was also observed in an adjacent duct carcinoma in situ component in 37/45 cases (82.2%). This study showed that MFAP5 is a novel myoepithelial cell marker that appears to be upregulated in duct epithelium in duct carcinoma in situ and invasive carcinoma of no special type during tumorogenesis and that its cytoplasmic expression in invasive tumors seems to have a poor prognostic role manifested by its association with poor prognostic parameters such as high grade, late stage, lymph node invasion, and increased microvessel density. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.