Spontaneous Eosinophilic Granulated Round Cell Tumors in Rats

Abstract

Morphologic and histochemical characteristics were noted for three spontaneous tumors with eosinophilic cytoplasmic granules that occurred in aged Fischer 344 rats. Macroscopic lesions were widely distributed in the body, mainly involving the intra-abdominal adipose tissue, pancreas, and mesenterium. These lesions were generally hard swellings with nodular and sclerosing areas. Bloody ascites was a concomitant finding. Histologically, the tumor cells were round, from 9 to 30 microm in diameter with one or two round to oval nuclei, and characterized by eosinophilic granules (0.5-2.0 microm) that stained definitely to weakly positive with the periodic acid-Schiff reaction and demonstrated no metachromasia with toluidine blue stain. Furthermore, the granules were characterized by a positive reaction with lectin histochemistry for concanavalin A (Con A), wheat germ agglutinin (WGA), phaseolus vulgaris agglutinin (PHA-E4), lens culinaris agglutinin (LCA), and recinus communis agglutinin (RCA-I) in all tumors and for ulex europaeus agglutinin (UEA-I), peanut agglutinin (PNA), and soybean agglutinin (SBA) in one tumor. Positive reactions for anti-rat mast cell protease II and CD8 were not demonstrated immunohistochemically. Abundant glycogen was noted in the large tumor cells from one rat. With electron microscopy, the cytoplasmic granules were identified as electron-dense homogenous bodies bounded by a single unit membrane. These characteristics are similar to those of granulated metrial gland cells, but further study is needed to clarify the cell of origin for these tumors.

The Metrial Gland in the Rat and Its Similarities to Granular Cell Tumors

“…Although the metrial gland has received attention in human endocrinology, immunology, and reproductive physiology literature, the metrial gland has rarely been mentioned in the veterinary or toxicologic pathology literature (Karbe et al 2000; Nagatani et al 2001; Yoshida 1997). The four most recent reports and characterizations of granular cell tumors of the rat and mouse genital tract (1) do not mention the GMG cell or metrial gland; (2) do not discuss the GMG as a possible cell involved in the proliferative lesion; and (3) do not entertain the possibility that proliferative lesions involving granular cells could be non-neoplastic (Courtney et al 1992; Markovits et al 2000; Nyska et al 1991; Veit et al 2008).…”

Spontaneous globule leukocyte tumor accompanied by inflammatory cells in a Wistar Hannover rat

“…Various histochemical and immunohistochemical stains and electron microscopic examination revealed that this neoplasm was a globule leukocyte tumor. While eosinophilic granulated round cell tumors 11 and an eosinophilic granulated cell tumor 12 with similar granules were previously reported in rats, the origin of these granulated cells was not clear. To our knowledge, no report has yet described a diagnosis of globule leukocyte tumor in rats.…”

Malignant mast cell tumor of the thymus in an Royal College of Surgeons (RCS) rat

“…Granular cell tumors and globule leukocyte tumors are characterized as round cell tumors with eosinophilic granules, similar to those observed in the current case. Accordingly, metachromasia, using toluidine blue, was required to confirm the diagnosis 1 , 2 , 13 , 14 .…”