Expression of estrogen receptors-α and β in chemically-induced mammary tumours

Abstract

Objective: Estrogen receptors (ERs)-α and β are important for stimulating the growth and differentiation of human mammary tumours, respectively. This work aimed to evaluate the expression of ERs-α and β in rat chemically-induced mammary tumours. Methods: Procedures followed the European legislation (2010/63/EU). Fifteen seven-week-old female Sprague-Dawley rats received an intraperitoneal injection of N-methyl-N-nitrosourea (MNU) (50mg/Kg). At sacrifice, mammary tumours were fixed and histologically evaluated. Sections were incubated with ER-α and β primary antibodies and the percentage of immunopositive cells was determined.

Results: During the experimental protocol four animals died, all survived animals developed mammary tumours: 30 benign, 2 preneoplastic and 39 malignant lesions. All histological patterns expressed ERs-α and β. The mean expression of ER-α (55.14% ± 13.26) was lower than the expression of ER-β (70.06% ± 18.51) (p<0.05). The expression of both receptors was not statistically different among lesions, however it was higher in preneoplastic lesions, followed by malignant and benign ones (p>0.05). Conclusion: All MNU-induced mammary tumours in rats expressed ERs-α and β, being a good model of ER-positive human mammary tumours. Once the expression of ER-β was higher, tumours’ differentiation was stimulated and its proliferation was inhibited.