Immunohistochemical Expression of Estrogen Receptor β in Normal and Tumoral Canine Mammary Glands

To date, two isoforms of estrogen receptors (ER) have been identified, cloned, and characterized from several species, estrogen receptor-α (ERα) and estrogen receptor-β (ERβ). Although the presence of ERα has been demonstrated in normal and tumoral canine mammary tissues, the issue of ERβ expression has not been addressed in the dog. In this study, we have analyzed the expression of ERβ in formalin-fixed, paraffin-embedded tissue samples of nonaltered mammary gland, 30 malignant (six complex carcinoma, 12 simple carcinoma, three carcinosarcoma, and nine carcinoma or sarcoma in benign tumor), and five benign (one fibroadenoma, one complex papilloma, one complex adenoma, and two benign mixed tumors) mammary tumors of the dog by using a polyclonal ERβ antibody and the avidin-biotin-peroxidase complex immunohistochemical technique. Our results show that high numbers of normal ductal and acinar epithelium and approximately one third of canine mammary tumors express ERβ. This expression was higher in benign than in malignant tumors. Furthermore, expression was higher in complex and mixed histologic subtypes of malignant tumors when compared with simple subtypes.