Introduction

Mammary tumors are the most prevalent tumor in bitches and the incidence of malignant mammary tumors in Brazil exceeds 70%. Metastasis development is one of the main causes of tumor-related death. Matrix metalloproteinases are capable of degrading type IV collagen, facilitating metastatic progression.

Objectives

Evaluate MMP-9 gene expression in benign and malignant canine mammary tumors.

Methods

Fresh normal mammary glands (n = 5), benign mammary tumors (n = 6), non-metastatic carcinoma (n = 18) and metastatic mammary carcinoma samples (n = 11) were evaluated for MMP-9 gene expression by RT-qPCR. The metastases of mammary carcinomas were located in regional lymph nodes, lung, liver, spleen and adrenal, but only primary tumors were evaluated. The patients of this study had a 2-year followup.

Results

High expression of MMP-9 was correlated with benign mammary tumors (p = 0,0087), non-metastatic mammary carcinomas (p = 0,0081) and metastatic mammary carcinomas (p = 0,0022) when compared to normal mammary glands. No statistical difference among benign tumor, non-metastatic and metastatic mammary carcinomas was observed (p > 0,05). Women studies have shown that MMP-9 gene expression is strongly associated with tumor metastasis and, in bitches, an increase of MMP-9 protein expression was found in malignant tumors.

Conclusions

Although benign tumors and non-metastatic carcinomas have shown increased expression of MMP-9 mRNA, higher levels were found in metastatic mammary carcinomas that can be an initial event in tumors to facilitate metastatic progress.

Grant 2013/03940-4, São Paulo Research Foundation (FAPESP)