Immunohistochemical Characterization of N-Methyl-N-Nitrosourea-induced Mammary Tumours of Sprague-Dawley Rats

Background: Single dose of N-methyl-N-nitrosourea (MNU) was shown to induce malignant tumours in susceptible rat strains. However, such tumours are not well-characterized. Material and Methods: We characterized MNU-induced tumours in Sprague-Dawley rats using ultrasonographic, radiographic and immunohistochemical (IHC) methods. Results: In 27 rats, 41 tumours developed, appearing ultrasonographically as hypodense, non-homogenic areas with signal enhancement at their peripheiy. Out of these, 39 were of malignant epithelial origin, with an IHC phenotype closely-resembling that of human invasive ductal breast carcinoma. One case was diagnosed as carcinosarcoma. IHC analysis revealed that Ki-67 antigen expression correlated positively with tumour volume (r=0.40, p=0.0079). Moreover, tumours with a-smooth muscle actin in the tumour stroma were characterized by a higher proliferative rate as compared to those without its expression (p<0.05). Conclusion: This rat model of chemical carcinogenesis may be suitable for examining breast cancer development and progression.