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Immunohistochemical expression of molecular markers in an avian model: a potential model for preclinical evaluation of agents for ovarian cancer chemoprevention.

OBJECTIVE
A significant obstacle confronting the evaluation of potential chemopreventive compounds in ovarian carcinoma is the absence of an animal model of spontaneous ovarian carcinogenesis. A potential model of adenocarcinoma has been described in the laying hen (Gallus domesticus). The purpose of this study was to evaluate the immunohistochemical expression of available antibodies that have been utilized in chemoprevention studies in this potential model of epithelial carcinoma.


METHODS
Two hundred 2-year-old hens were sacrificed at Auburn University in accordance with IUACUC guidelines. Of these hens, 8 animals were thought grossly to have ovarian carcinoma and ascites. The tumors from these 8 hens were fixed in neutral-buffered formalin and processed to paraffin blocks. Hematoxylin and eosin stains were used to document the histologic presence of adenocarcinoma. Immunohistochemical evaluation for expression of antigen was performed using the following antibodies: CA125, CEA, cytokeratin, EGFR, erbB-2, Ki-67, Lewis Y, p27, PCNA, Tag 72, TGF-alpha, Muc 1, and Muc 2.


RESULTS
Upon microscopic examination by a pathologist eight specimens were documented as adenocarcinomas. Several antibodies to antigens that are frequently expressed in human ovarian cancer were cross-reactive in the laying hen. Of these, cytokeratin AE1/AE3, pan cytokeratin, EGFR, Lewis Y, CEA, Tag 72, and erbB-2 stained the chicken carcinomas. EGFR and p185erbB-2 stained diffusely, and cytokeratin AE1/AE3, pan cytokeratin, Lewis Y, CEA, and Tag 72 were focally positive in the tumor. The aforementioned antibodies which have been useful as surrogate endpoints in chemoprevention trials and which also stained the chicken carcinomas included PCNA, p27, and TGF-alpha Antibodies that were not cross-reactive include CA 125, Ki-67, Muc 1, and Muc 2.


CONCLUSION
The data presented in this pilot study support the potential utility of an avian model of spontaneously arising adenocarcinoma in which to study chemopreventive agents. More importantly, the influence of chemoprevention protocols on the expression of relevant antigens can be determined using available antibodies that are cross-reactive in this model. Thus, changes in the phenotypic expression of surrogate endpoint biomarkers as identified by cross-reactive antibodies can aid in the development of chemoprevention trials for human ovarian cancer.