Invasive ductal carcinoma of the mammary gland in a mare.

This study documents the case of a 21-year-old mare that suffered from an invasive ductal carcinoma – a type of breast cancer – that spread to multiple organs. The neoplasms within the tumor were analyzed and classified based on their structure and reactions to various immunohistochemical tests.

Disease Identification and Pathology

• The mare was found to have a large mass (35 x 14 x 10 cm) residing within the mammary gland. This tumor was not isolated; metastases, or areas where the cancer had spread, were found in the kidneys, lungs, skeletal muscles, and regional lymph nodes.
• Histopathologic examinations were conducted on the tumor. It was discovered to be a ductal solid carcinoma, which is a common type of breast cancer that emerges from the ducts of the mammary gland. This specific case also showed extensive intraductal and intralobular involvement. This means that the tumor was not limited to the ducts, but it had invaded both the channels that lead milk towards the nipple (ducts) and the segments of the gland where milk is produced (lobules).

Microscopic Examination and Immunochemistry

• At a microscopic level, the neoplasms were divided into irregularly shaped islands and sheets of polygonal and spindle-shaped epithelial cells surrounded by fibrous connective tissue bundles. These neoplastic cells had a small to moderate amount of cytoplasm and round or oval nuclei that stained heavily when exposed to eosin, a common histological stain.
• Immunohistochemical tests were conducted using various markers, which revealed different degrees of positivity or negativity in the neoplastic cells. For instance, the cells were strongly positive for Lu-5 – a marker of breast cancer, while weaker results were observed for AE1/AE3, vimentin, and Glial Fibrillary Acidic Protein (markers of different cell types). They were negative for cytokeratin 8, cytokeratin 14, alpha-smooth muscle actin, calponin, and S100, indicating that the cells lack these particular proteins.

Final Diagnosis

• Following the extensive investigations and tests, the tumor was finally classified as an invasive ductal carcinoma of the mammary gland. The term ‘invasive’ implies it is not confined to its place of origin and has the capacity to invade surrounding tissues or organs. In this case, it led to multiple metastases, illustrating the aggressive nature of the disease.