• Open Access

Aglepristone Decreases Proliferation in Progesterone Receptor-Positive Canine Mammary Carcinomas


  • This work was done at the Department of Comparative Pathology of the Veterinary Faculty of the University of Córdoba, Córdoba, Spain and the Institute of Veterinary Pathology, Vetsuisse-Faculty, University of Zurich, Zurich, Switzerland. This work was presented at the 28th Meeting of the European Society of Veterinary Pathology, September 2010, Belgrade, Serbia; and the Veterinary Cancer Society Meeting, October 2010, San Diego, CA.

Corresponding author: Juana Martín de las Mulas, Department of Comparative Pathology, Veterinary Faculty, University of Córdoba, Edificio de Sanidad Animal, Campus de Rabanales, Carretera de Madrid-Cádiz Km, 396 14014 Córdoba, Spain; e-mail: an1magoj@uco.es.


Background: Progesterone receptor (PR) antagonist aglepristone (RU534) has been used successfully for pregnancy termination and therapy of pyometra, vaginal tumors, and mammary hyperplasia in bitches and queens. All of these conditions share with canine mammary carcinomas the expression of PR.

Objectives: To study the effect of RU534 on proliferation and apoptosis in canine mammary carcinomas in relation to PR expression.

Animals: Twenty-seven nonspayed bitches with mammary carcinomas were treated with either 2 doses of 20 mg/kg RU534 (n = 22, RU534-treated group) or oil placebo (n = 5, control group) on days 1 and 8.

Methods: Tumor samples were collected before (day 1) and after (day 15) treatment for immunohistochemistry. PR expression, proliferation index (PI), and apoptotic index (AI) were determined using antibodies against PR, Ki67, and cleaved lamin A/C antigens, respectively. The effect of treatment on these parameters was analyzed.

Results: Differential expression of PR between day 1 (59.1% PR-positive tumors) and day 15 (36.4% PR-positive tumors) was observed in RU534-treated tumors exclusively. After RU534 treatment, mean PI was significantly decreased in PR-positive but unchanged in PR-negative RU534-treated tumors. A reduction of ≥20% in PI was found in 61.5% of RU534-treated tumors with PR expression. Conversely, no effect on AI was observed after RU534 treatment.

Conclusions and Clinical Importance: Neoadjuvant RU534 treatment had PR expression-related inhibiting effects on proliferation of canine mammary carcinoma cells.