A prospective analysis of immunohistochemically determined estrogen receptor alpha and progesterone receptor expression and host and tumor factors as predictors of disease-free period in mammary tumors of the dog.

The immunohistochemically determined estrogen receptor (ER) alpha (ERalpha) and progesterone receptor (PR) status, as well as recognized, well-accepted prognostic indicators and host factors were prospectively analyzed in 84 cases of primary canine mammary carcinoma for their effect on disease-free period (recurrence free, metastasis free, or combined) (DFP) after an observation period of 18 months. The presence of one or both receptors, as well as tumor size, lymph node status, histologic grading, intravascular growth, and necrosis, were of prognostic value for DFP. In multivariate analysis, only tumor size and histologic grading proved to be independent prognosticators. None of the host factors analyzed were of prognostic value for DFP. ERalpha, PR, or both were detected in 173 out of 228 tumors: 70 ERalpha and PR; 5 ERalpha only; 98 PR only. Statistically significant differences regarding the presence of one or both receptors were observed between benign and malignant tumors and between complex, mixed, and simple histologic subtypes of benign and malignant tumors. In the group of malignant tumors (n=155), the presence of one or both receptors was more frequent in tumors smaller than 3 cm, without lymph node metastasis, with tubulopapillary rather than solid patterns of growth among simple carcinomas, of histologic grades I and II, without both intravascular growth and necrosis, and with lymphocyte cell infiltrates. The most frequent groups of hormone receptors-positive tumors were the ERalpha-positive and PR-positive group among benign and the ERalpha-negative and PR-positive group among malignant tumors.