Immunohistologic Detection of Estrogen Receptor Alpha in Canine Mammary Tumors: Clinical and Pathologic Associations and Prognostic Significance

Abstract

Eighty-nine canine mammary tumors and dysplasias of 66 bitches were investigated to determine the immunohistochemical expression of classical estrogen receptor (ER-α) and its clinical and pathologic associations and prognostic value. A complete clinical examination was performed and reproductive history was evaluated. After surgery, all animals were followed-up for 18 months, with clinical examinations every 3–4 months. ER-α expression was higher in tumors of genitally intact and young bitches ( P < 0.01, P < 0.01) and in animals with regular estrous periods ( P = 0.03). Malignant tumors of the bitches with a previous clinical history of pseudopregnancy expressed significantly more ER-α ( P = 0.04). Immunoexpression of ER-α decreased significantly with tumor size ( P = 0.05) and skin ulceration ( P = 0.01). Low levels of ER-α were significantly associated with lymph node involvement ( P < 0.01). Malignant tumors had lower ER-α expression than did benign tumors ( P < 0.01). Proliferation index measured by proliferating cell nuclear antigen immunostaining was inversely correlated with ER-α scores ( P = 0.05) in all tumors. Low ER-α levels in primary malignant tumors were significantly associated with the occurrence of metastases in the follow-up ( P = 0.03). Multivariate analyses were performed to determine the prognostic significance of some follow-up variables. ER-α value, Ki-67 index, and age were independent factors that could predict disease-free survival. Lymph node status, age, and ER-α index were independent prognostic factors for the overall survival. The immunohistochemical detection of ER-α in canine mammary tumors is a simple technique with prognostic value that could be useful in selecting appropriate hormonal therapy.