Canine perianal gland carcinoma-associated antigens defined by monoclonal antibodies

This study was conducted to distinguish canine perianal gland carcinomas from adenomas using monoclonal antibodies (MAbs). The adenomas generally retain the lobular architecture, but some may contain focal areas of cellular pleomorphism. These changes may suggest malignant transformation and have led to discordant interpretations. To address this histopathological confusion, two perianal gland carcinoma-associated antigens were defined by mouse MAbs 4A9 and 1A10. These MAbs, generated against a canine mammary carcinoma cell line, reacted strongly with perianal gland carcinoma in preliminary screening and therefore were selected for further investigation. Cellular expression of antigens was examined by indirect immunoperoxidase (IP) assay using MAbs 4A9 and 1A10 against formalin-fixed, paraffin-embedded sections of normal and tumor tissue. Of 25 perianal gland carcinomas, 4A9 antigen was expressed in 100% and 1A10 antigen in 84%. In contrast, perianal gland adenomas were negative for both antigens, and little or no reactivity was detected with normal perianal glands. With eight perianal gland tumors, diagnosis of carcinoma versus adenoma was histologically equivocal, while IP assays consistently revealed focal expression of the 4A9 and 1A10 antigens in these tumors, and the staining coincided with foci of anaplastic cells having a high mitotic index. This group of tumors was designated adenoma/carcinoma in situ. Results suggest that 4A9 and 1A10 antigens are markers of carcinoma and malignant transformation in canine perianal gland tumors, and can be very useful as diagnostic reagents where the identification of carcinoma versus adenoma requires additional clarification beyond routine histopathological examination.