Immunohistochemical Determination of Estrogen and Progesterone Receptors in Canine Mammary Tumors

Mammary gland tumors are by far the most commonly found tumors in domestic dogs. Effective therapeuticprocedures with prompt accurate diagnoses are of prime importance for this life threatening neoplasm. Althoughimmunohistochemical methods provide valuable information such as the location and semi-quantitative data ofthe interested antigens in particular tumors, conventional methods like histopathological diagnosis remain usefuland necessary for identification and classification of tumors. In the present study, we combined histopathologywith immunohistochemical staining of estrogen receptors (ER) and progesterone receptors (PR) in caninemammary gland tumors. Fifty dogs with primary mammary tumors underwent surgery at the VeterinaryTeaching Hospital of Mahidol University during 2005 to 2007. Three of them were diagnosed with precancerouslesions and negatively stained for ER or PR antibody. Twenty one were diagnosed with benign tumors classifiedas adenomas and benign mixed mammary gland tumors. Nearly 60% of the lesions were negatively stained forER or PR. PR positively stained, both PR and ER stained and ER stained tumors accounted for 19%, 19% and5%, respectively. Of the malignant tumors, eighty-six percent were adenocarcinomas and 14% were malignantmixed mammary gland tumors. Nearly 70% were negatively stained for ER or PR, 14% were PR positivelystained, 14% were both PR and ER stained and 5% were ER stained. Four dogs had unidentified lesions. Insummary, more than half of our benign and malignant canine mammary tumors were negatively stained for ERand PR. This indicates a lack of correlation with estrogen and/or progesterone receptor expression.