Mammary tumors in pet rabbits. Immunohistochemical findings.

Introduction. Mammary adenocarcinomas are fairly common in female rabbits over 3 years of age and occur more frequently in entire breeding doe than in spayed family pet rabbits. In this study a series of 15 cases of mammary diseases in pet rabbits were investigated to demonstrate the role of known breast cancer biological phenomena in the progression of rabbits mammary tumours and their aids in therapeutic approach. Material and methods. Three hyperplastic mammary glands, 2 simple adenomas and 10 adenocarcinomas (9 simple tubulo-papillary and 1 mucinous) removed from 15 rabbits, were available as formalin fixed and paraffin wax embedded samples. Serial sections underwent ematoxylin-eosin and immunohistochemistry stains with the following panel of antibodies: proliferation-associated antigen Ki67 (clone MIB-1), estrogen receptor-α (ER-α), HER-2, telomerase (TEL) and E-cadherin (E-Cad). Comparisons between malignant and non-malignant (hyperplasia+adenomas) lesions were evaluated. Results. 80% of the non-malignant and 30% of the malignant cases were positive (cut off 10%) to ER-α (Chi square, P=0.06). A significant higher MIB1 index (percentage of positive nuclei) was recorded in carcinomas compared to non-malignant lesions (t-test, p= 0.011). HER-2 positivity (staining in more than 10% of neoplastic cells) was observed in 2/15 cases (one adenoma and one carcinoma). In 7 carcinomas E-Cad showed reduced expression with a cytoplasmic localization in 5 cases. Conclusion. In the rabbit a lower expression of hormone receptors and high proliferation activity characterizes the mammary carcinomas, in which low is the expression of HER-2 while TEL activation involves more than 50% of the cases. It seems that anti-proliferative and anti-telomerase therapeutic approach should be the most proper in rabbit mammary carcinomas.