Odontogenic keratocyst: role of immunohistochemisty in differential diagnosis and prognostic evaluation

Background: according to the latest Who classifica- tion (2017), odontogenic cysts are classified into 3 groups: malformative, inflammatory and neoplastic. the odontogenic keratocyst belongs to the neoplastic cyst group and arises from epithelial residue of dental foil; characterized by strong invasiveness it can be occur as a sporadic lesion or associated to the gorlin-goltz syndrome. the aim of the study was to evaluate the development and invasiveness of odontogenic keratocyst with immunohistochemical analysis of antigen, such as apoptosis and local invasiveness markers for the pur- pose of a correct diagnosis, as a therapeutic first step. MethoDS: 15 cases of odontogenic keratocysts, 9 sporadic and 1 related to gorlin-goltz syndrome lesions, and 10 cases of inflammatory and malformative cysts divided into 5 radicular, 3 follicular and 2 gingival were selected. 11 silane sections were obtained by selected pads and subjected to immunohis- tochemical analysis with antibodies for Ki-67, p63, p21, p53, bcl-2, β-catenina, CK19, CK8-18, CK17, STAT6, and EGFR. antigenic recovery was performed with Dako instrumentation (Pt link); tissue was treated in low or high ph buffer (depend- ing on antigen) for 20’ at 97°c. the following steps were then performed: PBS buffer for 5’, endogenous peroxidase inhibi- tion in h2 o2 at 3% for 10’ at room temperature, washing in PBS buffer, primary antibody incubation in wet room for 30’ at 5°, washing in PBS buffer for 10’, dextran polymer incuba- tion at room temperature for 20’, double washing PBS buf- fer, development of reaction by DaB, washing in PBS buffer, washing in distilled water, nuclear contrast with Mayer stain for 1-3’, washing in water for 5’, washing in alcohol increasing scale, xylol and synthetic resin mounting. reSUltS: all odontogenic keratocysts expressed cK19 in baseline and upper-baseline layer except in inflammatory areas with an irregular expression of cK19 and positivity to cK8 and cK18. the single case of keratocyst associated to the gorlin- goltze syndrome did not allow us to do diagnostic and predic- tive evaluations although it presented positivity to cK17 in the epithelium, not always expressed in the other cases. the Bcl-2 protein showed a peculiar distribution mainly in the baseline layer and was negative in areas affected by inflammatory pro- cesses. p53 expression was high in baseline and upper-baseline layers, in contrast with the other odontogenic cysts where it was negative,and related to the increasing growth fraction expressed by Ki-67. p63 expression demonstrated nuclear posi- tivity in baseline and intermediate layers; the same positivity showed lower intensity in those areas affected by inflamma- tion of the fibrous wall. the p21 protein showed low positiv- ity without any correlation with other cellular cycle proteins (p63, p53 e Ki-67). Stat-6 was negative in every case. egFr expression was weak and limited to those baseline layers hit by inflammation. β-catenin expression appeared localized in the membrane and involved the entire epithelium; it disappeared or was only localized in those areas affected by inflammation. conclUSionS: in view of the immunohistochemical analy- sis it would appear that odontogenic keratocyst presents an antigenic molecular pattern which is discernible from other odontogenic cysts, but it becomes similar to a radicular cyst when it is then affected by an inflammatory process. among all of selected antigens, Bcl-2 turned out to be the main specific marker in the odontogenic keratocyst diagnosis.