Malignant granulosa-theca cell tumor in a two-year-old Miniature Horse.

The study presents the diagnosis of a rare malignant tumor called granulosa-theca cell tumor in a two-year-old Miniature Horse, which showed symptoms including weight loss, depression, and diarrhea.

Summary of the Research

• This research focused on the case of a 2-year-old female Miniature Horse suffering from severe health conditions, including continuous weight loss, depression, and diarrhea. It turned out that the horse was suffering from a highly malignant abdominal neoplasm—a new and abnormal growth of cells that could form a tumor.
• The tumor was spread across numerous critical internal organs including the left ovary, kidneys, adrenal glands, intestines, and various lymph nodes within the abdominal and thoracic regions. The diagnosis of the exact nature of the neoplism was conducted after the animal had died, during a post-mortem examination (necropsy).

Microscopic Examination of the Tumor

• Upon microscopic examination of the masses, the researchers discovered large pleomorphic cells. Pleomorphism refers to a situation where cells assume varying sizes and shapes, which frequently occurs in malignant tumors.
• The cells in question showed a positive response for vimentin, an intracellular protein, and inhibin, a hormone secreted by gonads. However, they tested negative for epithelial membrane antigen (a marker for epithelial cells) and placental alkaline phosphatase (a cellular enzyme), both of which can be indicative of specific types of tumors.

Ultrastructural Examination and Diagnosis

• The ultrastructural examination, which refers to the detailed structural study of the cells under an electron microscope, depicted a high nucleocytoplasmic ratio and indented euchromatic nuclei with large nucleoli. High nucleocytoplasmic ratio implies more nuclear material relative to the cytoplasm, common in rapidly dividing cells like cancer cells.
• Based on the comprehensive analysis of the visible characteristics of tumor, microscopic and ultrastructural details, and the results of immunohistochemical tests (tests looking for presence of specific proteins in tissue samples), the neoplasm was diagnosed as a malignant granulosa-theca cell tumor, a rarely observed tumor in young horses. Granulosa-theca cell tumors originate from ovarian cells and their malignant form has a potential for aggressive growth and metastasis.