Introduction

Mammary gland tumors are the most common in domestic animals. Mammary gland tumors were reported in the Guinea pigs by some authors. This is the first report of the malignant mammary gland tumor in male Guinea pig with papillary type.

Objectives

A 3-year-old male Guinea pig with a lump in the left inguinal mammary gland was included in this study. The case was examined clinically and treated surgically in the Paytakht Pet Hospital. Clinical information and data on the reproductive history of the case were obtained from the owner at first presentation. These details included age, breed, body size, castration, and hormonal treatments.

Methods

After a complete physical examination, mammary glands and regional lymph nodes were examined to obtain information on tumour size, adhesion to surrounding tissues, and skin ulceration. Radiological examination of the thorax (two lateral projections) and abdominal sonography did not reveal detectable metastases. The size of the tumor was 2 cm x 1.5 cm. Tissue section was fixed in 10% buffered formalin and embedded in paraffin wax and stained with H & E.

Results

Cell population is composed of only one cell type, resembling either luminal epithelial cells or myoepithelial cells. Malignancy criteria like multiple nucleoli and high mitotic index were observed in gland epithelial cells. Mammary gland carcinoma (Grade III) with papillary form and lymphocyte infiltration was diagnosed. Mammary gland tumor was intensively positive to Ki-67 and P53 and mildly positive for ER-α and PR.

Conclusions

According to our knowledge, this is the first report of the malignant mammary gland tumor in a male Guinea pig.