The aggressive nature of the odontogenic keratocyst: is it a benign cystic neoplasm? Part 3. Immunocytochemistry of cytokeratin and other epithelial cell markers

Numerous studies of keratin expression by the more common odontogenic cysts were done to determine whether patterns of cytokeratin staining could provide accurate diagnostic markers for the different varieties; to see whether comparative studies with oral mucosa and developing odontogenic epithelium could explain the pathogenesis of the cysts; and whether cytokeratin patterns could provide clues in elucidating the aggressive nature of the OKC. This review was a complex task with a range of at least 19 different cytokeratins being studied and also a broad range of antibodies in use for the same cytokeratin or group of cytokeratins. Moreover, there was not always standardisation of laboratory techniques in the selection and preparation of material. These difficulties were, in general, recognised by the different workers in the field, particularly when there was disagreement on results and caution was expressed about drawing conclusions from some positive findings. It would be fair to conclude that cytokeratin immunocytochemistry has not advanced to any meaningful extent, its use as a diagnostic marker for the OKC nor in eludidating its pathogenesis. With regard to OKC behaviour, it has been pointed out that there was strong reaction of OKC lining for keratin 16, a cytokeratin that has been associated with high proliferative activity. Yet other studies have also shown keratin 16 expression in dentigerous and radicular cysts. Differences in cytokeratin, EMA and CEA immunocytochemical reactivity between the parakeratinised and orthokeratinised varieties of cyst were demonstrated and the suggestion made that the orthokeratinised type has a considerably less aggressive behaviour, is a different entity and should bear a different name. Furthermore, Ki67 positive cells in the parakeratinised OKC linings were considerably more frequent than in the orthokeratinised linings. OKC, dentigerous and radicular cyst epithelium reacted positively for epithelial growth factor receptor (EGFr) but a trend indicating the most intense staining in the OKCs, followed by the dentigerous and then the radicular cyst linings led to the conclusion that the OKCs have an intrinsic growth potential not present in other odontogenic cysts.