Abstract The purpose of the present study is to deter- mine the presence and distribution of epithelial and myo- epithelial cells in mucoepidermoid carcinoma (MEC) of salivary glands and to compare them with normal saliva- ry gland tissue and other primary carcinomas. This is in order to establish novel diagnostic criteria and to better understand MEC histogenesis. Formalin-fixed paraffin- embedded tissues from ten well-differentiated MECs, three adenoid cystic carcinomas (ACC), four acinic cell carcinomas (AC), and three epithelial-myoepithelial car- cinomas (EMCC) of salivary glands were studied with immunohistochemistry using antibodies that recognise antigens indicative of epithelial and myoepithelial cell differentiation. An anti-mitochondrial antibody was also employed. Normal salivary tissue was present for com- parative study in non-tumorous areas of the same section from 12 cases. MEC contained numerous keratin-posi- tive cells. Anti mitochondrial antibody was diffusely positive in all ten of these tumours. Smooth muscle ac- tin, h-caldesmon, and smooth muscle heavy chain myo- sin, which are indicative of myoepithelial cell differenti- ation, were negative. Rare cells in only one case were stained by calponin. Cytokeratin 14 (CK14) and anti mi- tochondrial antibody stained cells located mainly at the periphery of neoplastic nests and cystic spaces, while CK7 was mainly present in cells bordering gland lumina (zoning pattern). The immunohistochemical cell profile was similar to that seen in striated normal ducts. All others tumours studied showed a different immunohisto- chemical pattern, mostly consisting of a lack of mito- chondrion-rich cells and the presence of myoepithelial cells in ACC and EMCC. Immunoreactivity in MEC for CK7, CK14 and mitochondrial antibodies appears as a peculiar pattern of staining, different from that of other salivary gland tumors; this seems helpful for diagnostic purposes. In addition, a differentiation of the “striated duct phenotype” is suggested. Keywords Myoepithelial cell · Basal cell · Cytokeratin · Salivary gland · Mucoepidermoid carcinoma Introduction Mucoepidermoid carcinoma (MEC) of salivary glands is a tumor composed of several cell types. According to the accurate original description of Stewart et al. [29], MEC is mainly composed of mucous secreting, basa- loid, intermediate, and epidermoid cells. In addition, these authors found that clear and columnar cells can be present. After comparing MEC morphological features with those of non-neoplastic salivary glands involved by chronic inflammatory processes, they suggested an ori- gin from salivary gland ducts [29]. Most of the morpho- logical information about cellular differentiation of MEC resides in ultrastructural observations [3, 7, 8,]. Dardick et al. [7, 8] indicated that MECs consisted of two types of cells similar to those located along the aci- nar-intercalated ducts. Ultrastructural and immunohisto- chemical studies have demonstrated the presence of oc- casional myoepithelial cells in MEC [9, 17, 19, 24]. Re- cently, proteins related to the contractile function of smooth muscle cells, such as calponin, caldesmon, and smooth muscle heavy chain myosin have been demon- strated to be present in normal and neoplastic myoepi- thelial cells [5, 15, 23, 26, 30]. The purpose of the present study is to determine the presence and distribution of epithelial and myoepithelial cells in MEC and to compare these findings with normal salivary gland tissue and other primary carcinomas of the salivary glands. This was undertaken in order to estab- lish further diagnostic criteria and to better understand MEC histogenesis. M.P. Foschini ( ✉ ) · G. Marucci · V. Eusebi Department of Oncology, Section of Anatomic Pathology, “M. Malpighi”, University of Bologna, Ospedale Bellaria, Via Altura 3, 40139 Bologna, Italy e-mail: mariapia.foschini@ausl.bologna.it Tel.: +39-051-6225523, Fax: +39-051-6225759 Virchows Arch (2002) 440:536–542 DOI 10.1007/s00428-001-0585-6 ORIGINAL ARTICLE Maria P. Foschini · Gianluca Marucci Vincenzo Eusebi Low-grade mucoepidermoid carcinoma of salivary glands: characteristic immunohistochemical profile and evidence of striated duct differentiation Received: 22 October 2001 / Accepted: 6 November 2001 / Published online: 9 February 2002 © Springer-Verlag 2002