A New Subtype of Papillary Ductal Carcinoma in Situ with Tall Cell and Reversed Polarity Morphology: A Rare Case

Abstract Papillary ductal carcinoma in situ (DCIS) is a subtype of DCIS characterized by the neoplastic proliferation of epithelial cells with a papillary structure and confined to the mammary ductal-lobular system. Tall cell carcinoma with reversed polarity (TCCRP) is a rare subtype of invasive breast carcinoma with low malignant potential, which has recently been recognized as a separate entity in the 2019 WHO Classification of breast tumors. Here, we describe the case of a 54-year-old woman with a finding of growing nodular lesion through breast ultrasonographic screenings, whose morphological features, immunohistochemical results, and molecular genetic studies suggest overlapping features of DCIS and TCCRP. Therefore, we hypothesized that it might be a new DCIS subtype with tall cells and reversed polarity of the mammary gland.