Immunohistologic detection of estrogen receptor alpha in canine mammary tumors: Clinical and pathologic associations and prognostic significance

Eighty-nine canine mammary tumors and dysplasias of 66 bitches were investi gated to determine the immunohistochemical expression of classical estrogen receptor (ER-alpha) and its clinical and pathologic associations and progn ostic 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-alpha expression wa s hi her in tumors of genitally intact and young bitches (P < 0.01, P < 0.0 1) and in animals with regular estrous periods (P = 0.03). Malignant tumors of the bitches with a previous clinical history of pseudopregnancy express ed significantly more ER-alpha (P = 0.04). Immunoexpression of ER-alpha dec reased significantly with tumor size (P = 0.05) and skin ulceration (P = 0. 01). Low levels of ER-alpha were significantly associated with lymph node i nvolvement (P < 0.01). Malignant tumors had lower ER-alpha expression than did benign tumors (P < 0.01). Proliferation index measured by proliferating cell nuclear antigen immunostaining was inversely con-elated with ER-alpha scores (P = 0.05) in all tumors. Low ER-alpha levels in primary malignant tumors were significantly associated with the occurrence of metastases in t he follow-up (P = 0.03). Multivariate analyses were performed to determine the prognostic significance of some follow-up variables. ER-alpha value, Ki -67 index, and age were independent factors that could predict disease-free survival. Lymph node status, age, and ER-alpha index were independent prog nostic factors for the overall survival. The immunohistochemical detection of ER-alpha in canine mammary tumors is a simple technique with prognostic value that could be useful in selecting appropriate hormonal therapy.