Spontaneous equine pulmonary granular cell tumors: morphologic, histochemical, and immunohistochemical characterization.

The research article discusses a study on spontaneous equine pulmonary granular cell tumors found in six horses. The study elaborates on the physical appearance, cellular characteristics, chemical responses, and similarity of these tumors to human endobronchial granular cell tumors.

Objective of the study

The aims of the study were:

• To diagnose and study spontaneous equine pulmonary granular cell tumors in six mature horses
• To accurately present the physical appearance of these tumors
• To investigate the location and influence of these tumors on airways
• To describe the cellular characteristics through histochemical and immunohistochemical analysis
• To compare the morphological aspects of these tumors to human endobronchial granular cell tumors.

Studies and Findings

The study found that:

• The tumors were noticeable as multiple or single white, firm nodules
• These tumors were situated near bronchi and bronchioles and often invaded airways, causing partial to full blockage of the lumina
• The examined cells were rounded to polyhedral, packed with eosinophilic cytoplasmic granules. These granules invariably reacted positively with S-100 and neuron-specific enolase antibodies, and sporadically with glial fibrillary acidic protein antibodies.
• These cells were found to be negative for muscle-specific actin, lysozyme, cytokeratin, chromogranin A, and myelin basic protein antigens
• No staining occurred with silver by the Grimelius technique
• Consistent blue-green and random pink intracytoplasmic granules were visible with luxol fast blue and periodic acid-Schiff counterstain for myelin and myelin breakdown products

Conclusions from the study

By analyzing histochemical and immunohistochemical staining results, it was suggested that these tumors were made up largely of myelinating Schwann cells, with a smaller quantity of scattered non-myelinating Schwann cells. The morphological characteristics of these equine pulmonary granular cell tumors bear a striking similarity to human endobronchial granular cell tumors.