Immunohistochemical study of the orthokeratinized odontogenic cyst: A comparison with the odontogenic keratocyst Mario James A. da Silva, DDS, PhD, a Suzana Orsini Machado de Sousa, DDS, PhD, b Luciana Corre ˆa, DDS, PhD, c Artur Aburad Carvalhosa, DDS, d and Vera Cavalcanti de Arau ´jo, DDS, PhD, e Sa ˜o Paulo, Brazil UNIVERSIDADE DE SA ˜ O PAULO Objective. Orthokeratinized odontogenic cyst (OOC) is a developmental cyst that occurs in the maxilla and the mandible and is defined by the World Health Organization as the uncommon orthokeratinized type of odontogenic keratocyst (OKC). However, studies have shown that OOC has peculiar clinicopathologic aspects and biologic behavior when compared with other developmental odontogenic cysts, especially OKCs. Therefore, in this study, the immunohistochemical profile of the OOC was delineated and compared with that of the OKC. Study design. Twelve cases of OOC were submitted to a panel of antibodies composed of cytokeratins (10, 13, and 14) and extracellular matrix proteins: fibronectin, types I and III collagen, and tenascin. For comparative means, 12 cases of OKC also were submitted to the same panel of antibodies. Results. The results obtained showed that OOCs expressed cytokeratin 10 and showed variable expression of cytokeratins 13 and 14. Fibronectin and collagen types I and III also were expressed in OOC in a fibrillar aspect. OKC showed only the superficial keratin layer positive to cytokeratin 10 and the basal and suprabasal layers with variable expression of cytokeratin 14, and cytokeratin 13 was present in the upper epithelial layers. The extracellular matrix proteins showed a nonfibrillar expression. Tenascin was immunoexpressed only in OKC. Conclusion. The immunohistochemical profile of the studied cysts clearly showed that OOC presents a well-formed cystic enveloping, whereas the OKC profile is compatible with a more aggressive biologic behavior. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:732-7) The orthokeratinized odontogenic cyst (OOC) was first described by Schultz 1 in 1927 as a dermoid cyst, and in 1945, it was considered by Philipsen 2 as an eventual type of odontogenic keratocyst (OKC). In 1981, Wright 3 specified its clinicopathologic aspects, assuring that OOC was an individual entity, distinct from other odontogenic cysts, including the OKC. After that, a considerable number of studies have discussed the real nature and histopathologic classification of OOC. 4-10 OOC has been described as a solitary lesion, usually small and nonexpanding, radiolucent, and asymptom- atic, usually occurring in the posterior mandible of white patients between the fourth and fifth decades without gender predilection. OKC occurs mainly in the second and third decades with a mild predilection for men. Usually, OKCs are single lesions, unless they are associated with basal nevoid syndrome. In contrast to OKCs, the OOC has no tendency to recur and is not associated with the nevoid basal cell carcinoma syn- drome. 7 This study was undertaken to delineate possible dif- ferences between the tissue components of OOC and OKC. For this purpose, the immunoprofile of the epi- thelial lining for various molecular weight cytokeratins and the immunoprofile of the extracellular matrix pro- teins of the cystic wall were evaluated in both cysts. MATERIAL AND METHODS Twelve cases of OOC and 12 cases of OKC were retrieved from the files of the Oral Pathology Service of the School of Dentistry at the University of Sa ˜o Paulo. Criteria for selection of the OOCs were based on those established by Wright, 3 but the only cases included in the study were those in which epithelial lining was completely orthokeratinized and noncorrugated, with a granular layer that extended through all the epithelial length, and in which spinous and basal layers were not prominent. Immunostaining was carried out with the streptavidin-biotin method on dewaxed tissue sections. Sources, clones, concentrations, incubation periods of the primary monoclonal antibodies, and antigen retriev- als used for each antibody are summarized in Table I. a Professor, Department of Oral Pathology, Federal University of Ceara ´, Sa ˜o Paulo. b Associate Professor, Department of Oral Pathology, University of Sa ˜o Paulo. c Trainee, Department of General Pathology, University of Sa ˜o Paulo. d Graduate Student, Department of Oral Pathology, University of Sa ˜o Paulo. e Chairman, Department of Oral Pathology, University of Sa ˜o Paulo. Received for publication Jan 9, 2001; returned for revision Dec 4, 2001; accepted for publication Mar 12, 2002. © 2002, Mosby, Inc. 1079-2104/2002/$35.00 + 0 7/14/125199 doi:10.1067/moe.2002.125199 732