Comparative Immunohistochemical Study of Canine Mammary Tumours: Introducing of Triple-Negative Profile (ER-/PR-/HER2-) in Benign Mammary Tumours of Animal Model.

BACKGROUND

Mammary tumours are the most common neoplasm in female dogs. Canine mammary tumours (CMTs) are appropriate models for human studies.

OBJECTIVES

The present study aimed to diagnose CMTs pathologically and compare different tumour types by immunohistochemistry (IHC).

METHODS

Histological features of various tumours were recorded. Moreover, haematological, biochemical and immunohistochemical changes were evaluated in affected animals.

RESULTS

Among 130 mastectomized dogs in veterinary hospitals in Tehran, Iran, 74 dogs were affected by various types of mammary tumours. The highest frequency of malignant tumours was related to carcinoma types (38/74; 51.4%) and the highest frequency of benign tumours was related to fibroadenoma (6/74; 8.1%). In malignant tumours, anaemia and monocytosis were observed compared to benign tumours. Serum ALT and ALP levels were also significantly increased in malignant tumours (p < 0.05) compared to benign tumours. The IHC showed the profile of adenoma (ductal and intraductal papillary) ER+/PR-/HER2-, benign mixed tumour ER-/PR-/HER2-, carcinoma (mucinous, anaplastic) ER-/PR-/HER2- and metastatic mast cell tumour ER-/PR+/HER2-. The highest expression of αSMA was recorded in benign tumours and the highest expression of Ki67 was recorded in metastatic mast cell tumour, benign mixed tumour and adenoma (p < 0.05).

CONCLUSION

Together, although the dog is a good model for studying mammary tumours, the variability of results in CMTs requires further studies in this field. An interesting finding of this study was the triple-negative profile in the benign mixed tumour, which had previously been reported only for malignant mammary tumours. In addition, the significant positivity of Ki67 expression (34%-66%) in benign CMTs is noted for the first time.