Online Articles: Case ReportsA New Hitherto Unreported Histopathologic Manifestation of Mammary Analogue Secretory Carcinoma: “Masked MASC” Associated With Low-grade Mucinous Adenocarcinoma and Low-grade In Situ Carcinoma ComponentsPetersson, Fredrik MD, PhD*; Michal, Michael MD†; Kazakov, Dmitry V. MD†; Grossmann, Petr PhD†; Michal, Michal MD† Author Information *Department of Pathology, National University Health System, Singapore, Singapore †Department of Pathology, Medical Faculty in Pilsen, Charles University in Prague, Plzen, Czech Republic The authors declare no conflict of interest. Reprints: Fredrik Petersson, MD, PhD, Department of Pathology, National University Health System, 5 Lower Kent Ridge Road, Singapore 119074, Singapore (e-mail: [email protected]). Applied Immunohistochemistry & Molecular Morphology: October 2016 - Volume 24 - Issue 9 - p e80-e85 doi: 10.1097/PAI.0000000000000320 Buy Metrics Abstract We present a salivary gland tumor of the parotid gland in a 54-year-old woman, which contained a minor mammary analogue secretory carcinoma (MASC) component (20%) intermixed with a morphologically entirely different mucinous adenocarcinomatous component that comprised 80% of the tumor mass and a morphologically nondescript low-grade intraductal carcinoma (in situ) component. On fluorescence in situ hybridization, a break in the ETV6 gene was documented in the mucinous adenocarcinomatous, the conventional MASC, and the intraductal (in situ) components. RT-PCR failed to reveal an ETV6-NTRK3 fusion. The entire conventional MASC and only rare mucinous adenocarcinoma tumor cells were mammaglobin positive, whereas the low-grade intraductal carcinoma (in-situ) component was negative. S-100 protein stained only the MASC component. Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.