Non-functional C-cell adenoma in aged horses

Area of Science:

• Veterinary Pathology
• Equine Neoplasia
• Endocrinology

Background:

• Equine thyroid tumors are common in older horses, often presumed to originate from follicular epithelial cells.
• Limited immunohistochemical data exists for characterizing these equine thyroid neoplasms.
• Previous assumptions about tumor origin lack detailed investigation.

Purpose of the Study:

• To investigate the origin of equine thyroid tumors, specifically testing the hypothesis that they are parafollicular cell (C cell)-derived adenomas.
• To evaluate the pathogenesis and functional status of these equine thyroid tumors.
• To provide immunohistochemical characterization of equine thyroid lesions.

Main Methods:

• Histological, immunohistochemical, and ultrastructural examination of thyroid glands from 38 horses (aged 10-29 years).
• Evaluation of nodular tumor masses identified in the thyroids of horses.
• Immunohistochemical staining for calcitonin, neuron-specific enolase, and thyroglobulin.

Main Results:

• Nodular lesions were found in 31.6% of horses >10 years and 75.0% of horses >20 years.
• Tumor cells were positive for calcitonin and neuron-specific enolase, but negative for thyroglobulin.
• Ultrastructural analysis revealed minimal secretion granules in tumor cells.

Conclusions:

• The nodular thyroid lesions in older horses are identified as C-cell adenomas, not follicular adenomas.
• These equine C-cell adenomas are suspected to be non-functional.
• The tumors are unlikely to cause diseases related to calcitonin hypersecretion.