An Immunohistochemical Study on the Expression of Sex Steroid Receptors in Canine Mammary Tumors

Steroid hormones are found to play a major role in the genesis and progression of mammary tumors. The aim of this study was to immunohistochemically detect the presence of estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and progesterone receptor (PR) and also to study the association between these markers in 29 cases of benign (11) and malignant (18) canine mammary tumors. ERα immunostaining was noticed in only one case of carcinosarcoma specifically in the nuclei of epithelial and a few myoepithelial cells. ERβ immunostaining was noticed in the nuclei and cytoplasm of epithelial cells and smooth muscles lining the blood vessels. Immunoexpression of ERβ was 82% in benign tumors and 78% in malignant tumors. PR immunostaining was expressed in the nuclei of epithelial cells in both benign and malignant tumors. Among the 15 PR+ cases, 6 (55%) were of benign type, and 9 (50%) were of malignant type. The most common group of hormone receptor was the ERα？/PR+/ERβ+ (46%) in benign tumors and ERα？/PR？/ERβ+ (38%) in malignant tumors. Although there was no significant association between ERα and PR with ERβ, the findings indicated that ERβ was consistently expressed in both benign and malignant tumors, irrespective of ERα and PR status. 1. Introduction Mammary gland tumors are among the most common neoplasms in dogs and have been reported worldwide. The majority of mammary neoplasms in female dogs are of epithelial origin, and approximately 50% of them are malignant [1]. These neoplasms have a complex morphology in forming epithelial, mixed, and mesenchymal types [2]. Histologic evidence of cancer does not invariably imply a malignant clinical course. Therefore, reliable prognostic factors are of great importance for estimating the individual risk of unfavourable clinical outcome. There are some recognized, well-accepted prognostic factors of malignant mammary neoplasms in the dog, and these include tumor size, lymph node status, histologic type, histologic malignancy grade, degree of nuclear differentiation, and distant metastasis. There are also other proven or controversial host and tumor prognostic factors such as HER-2, p53, PCNA, and Ki-67, and the number of new ones are steadily increasing [3]. Although several studies have been carried out on the prognostic aspects of canine mammary neoplasms, some areas, especially the role of steroid hormone receptors, remain uncertain [4]. The risk of canine mammary neoplasia is affected by exposure to estrogen in early mammary development. The relative risk for mammary neoplasms in female dogs spayed