Histologic and immunohistochemical studies of granular cell tumors in seven dogs, three cats, one horse, and one bird.

The research article discusses a retrospective study where granular cell tumors in various animals – seven dogs, three cats, a horse, and a bird – were evaluated histologically and immunohistochemically. This process determined that these tumors, despite sharing morphological similarities, could come from different cellular origins.

Details of the Study

• The researchers conducted a retrospective study on granular cell tumors in various animals. These animals included six dogs (referred to as Nos. 1-6), three cats (Nos. 1-3), one horse (No. 1), and a cockatiel bird (No. 1). Additionally, they also examined a meningioma (a type of brain tumor) with a granular cell component in another dog (No. 7).
• All these tumors were identified through histological examination of surgical biopsy specimens, except for the one in the horse which was identified at necropsy unintentionally. At least two pathologists were involved in making the initial diagnoses.

Location and Histological Characterization of the Tumors

• The majority of the granular cell tumors in dogs were located in the oral cavity. The tumors found in cats were in different locations: the tongue, vulva, and on a digit. In contrast, the tumor in the horse was found in the lung while the cockatiel’s tumor was located in the periocular tissue (near the eye).
• On a histological level, these tumors were classified by their appearance as oval to polygonal cells of varying sizes. These cells consisted of an abundance of pale, eosinophilic cytoplasm with noticeable intracytoplasmic granules, distinct cell margins, and mainly central nuclei.

Particular Distinguishing Features and Reactions of the Tumors

• Certain distinct characteristics and reactions were seen in different tumors across the studied animals. For instance, in one of the dogs, the tumor found in the oral cavity contained a significant amount of collagen tissue. In another dog, the tumor found in the tongue displayed dilated blood vessels.
• All the granular cell tumors exhibited intracytoplasmic granules that stained with periodic acid-Schiff and were resistant to diastase enzyme. When stained with Luxol fast blue, the granules in all of the tumors, excluding one from a cat’s tongue, stained variations of pink – the exceptional tumor staining bluish-green.

Immunocytochemical Evaluations

• Immunocytochemical investigations revealed that all tumors, barring the one from the cockatiel, reacted against antibodies to vimentin, a type of protein filament involved in cell structure and integrity. This highlights the different cellular origins of these tumors, despite their similar morphology.

In conclusion, the study findings propose that granular cell tumors, alike to tumors consisting of rhabdoid cells, clear cells, and oncocytes, might have parallel morphologic traits but originate from different cell types.