The area of usual ductal hyperplasia from samples obtained from 18 patients with IPUDH whose tumor was also removed surgically during the same period was used as a control. The patients with SPC in situ who were selected to participate in this study showed some or all of the histological features of SPC in situ as described by Cross et al.1 and Tsang and Chan.2 All samples were positive for either chromogranin A or synaptophysin, or showed positive Grimelius staining. Immunohistochemical analysis Immunohistochemical staining of paraffin-embedded tissue was performed using antibodies to the following: chromogranin A, synaptophysin, CK5/6, CK14, and CK34betaE12 (which recognizes CKs 1, 5, 10, and 14). Table 1 shows a list of the sources and dilutions of these antibodies. patients with IPUDH. In tissues from patients with IPUDH, significantly more cells were stained with CK34betaE12 than CK5/6 ( em p /em ? ?0.05) or CK14 ( em p /em ? ?0.05). Conclusion: The immunoreactivity of CK5/6, CK14, and CK34betaE12 antibodies was useful to differentiate solid papillary carcinoma in situ from IPUDH. CK34betaE12 is especially useful for distinguishing solid papillary carcinoma from IPUDH. strong class=”kwd-title” Keywords: Breast, high-molecular-weight cytokeratin, immunohistochemistry, solid papillary carcinoma, intraductal papilloma Introduction Solid papillary carcinoma (SPC) in situ is a noninvasive ductal carcinoma with neuroendocrine differentiation that was first characterized by Cross et al.1 in 1985. More detailed reports were later published by Tsang and Chan2 and Kawasaki et al.3 The incidence of SPC in situ is accepted as 6.8%C23.3%1,3 of all cases of ductal carcinoma in situ (DCIS). Many patients are elderly,2 and bloody nipple discharge is a common symptom.3 Histopathologically, SPC in situ shows a solid growth pattern that includes a fibrovascular core in the dilated duct.1,2 The tumor cells are polygonal, oval, or spindle shaped with well-defined cell borders1,2 and granular acidophilic cytoplasm.2 The extracellular mucin TRi-1 in the microglandular spaces and septa are stained by periodic acid-Schiff, mucicarmine, and Alcian blue, which indicates that the mucin is of epithelial origin.2 SPC in situ is a TRi-1 malignant tumor that is difficult to differentiate from benign lesions Cd247 such as epitheliosis, intraductal epithelial hyperplasia, and florid hyperplasia, because proliferation of duct cells of those benign lesions resembles those of SPC in situ.1,2,4C6 The breast duct comprises two types of cells: duct and myoepithelial cells. However, some cells cannot be classified into either cell type. These cells are called stem cells/ progenitor-like cells and have the potential to differentiate into either duct cells or myoepithelial cells.7 Many properties, markers, or cell populations are used to identify breast stem cells including cytokeratin 5 (CK5),7 p21,8 Musashi 1,8 CK19,9 alfa6 integrin (CD49f),10 side population cells,8,11 label-retaining cells,8 epithelial specific antigen-positive/Muc1-negative cells,9,10 and epithelial membrane antigen-positive/common acute lymphoblastic leukemia antigen-negative cells.11 SPC in situ is a specific type of DCIS and should be differentiated from intraductal papilloma with usual ductal hyperplasia (IPUDH). CK5/6 and CK34betaE12 include CK5 as progenitor cell marker. TRi-1 CK14 is a component of one tetramer that is composed of two CK5s and two CK14s.12 In this study, we examined whether staining with antibodies of CK5/6, CK34betaE12, and CK14Crelated progenitor cell marker (CK5) could differentiate between SPC in situ and IPUDH. Materials and methods Patients and tumors This study included 18 consecutive patients with SPC in situ from the 211 DCIS patients (18/211, 8.5%) who had a tumor removed surgically at St. Marianna University Hospital (Kawasaki, Japan) from April 2003 to March 2009. One patient was excluded because the specimen obtained provided insufficient material for immunohistochemical staining. The area of usual ductal hyperplasia from samples obtained from 18 patients with IPUDH whose tumor was also removed surgically during the same period was used as a control. The patients with SPC in situ who were selected to participate in this study showed some or all of the histological features of SPC in situ as described by Cross et al.1 and Tsang and Chan.2 All samples were positive for either chromogranin A or synaptophysin, or showed positive Grimelius staining. Immunohistochemical analysis Immunohistochemical staining of paraffin-embedded tissue was performed using antibodies to the following: chromogranin A, synaptophysin, CK5/6, CK14, and CK34betaE12 (which recognizes CKs 1, 5, 10, and 14). Table 1 shows a list of the sources and dilutions of these antibodies. Immunoreactions were visualized using the avidinCbiotinylated peroxidase complex method. Table 1. Sources and dilutions of antibodies to chromogranin A, synaptophysin, CK5/6, CK14, and CK34betaE12. thead th align=”left” rowspan=”1″ colspan=”1″ Antibody /th th rowspan=”1″ colspan=”1″ /th th align=”left” rowspan=”1″ colspan=”1″ Source /th th align=”left” rowspan=”1″ colspan=”1″ Dilution /th /thead Chromogranin APolyclonalDako1:1SynaptophysinClone SY38Dako1:100CK5/6Clone D5/16 B4Dako1:20CK14Clone LL002Novocastra1:11CK34betaE12Clone 34betaE12Nichirei1:1 Open in a separate window Scoring of TRi-1 sections Using the 0C5 proportional scoring method of Allred et al.,13 we estimated the percentages of immunohistochemically stained tumor-like cells in hyperplastic lesions of duct cells, excluding myoepithelial cells. A score of 0 corresponded to 0%; 1,? 1%; 2, TRi-1 1% to 10%; 3, 10% to 33.3%; 4, 33.3% to 66.7%; and 5, ?66.7%. Cutoff score The.