Gastrointestinal stromal tumors with Kit gene mutation in 4 guinea pigs (Cavia porcellus).

Gastrointestinal stromal tumors (GISTs) have been rarely reported in guinea pigs. We aimed to characterize the clinical and pathological features of GISTs in 4 guinea pigs and investigate the presence of mutations in exon 11 of the KIT proto-oncogene receptor tyrosine kinase (Kit) gene. Two subjects were male and 2 were female; 2 were 6 years old, 1 was 7 years old, and 1 was of an unknown age. Three cases had primary gastric tumors, whereas 1 had a primary small intestinal tumor. All cases had tumors that extended from the submucosa to the serosa with extraluminal growth. A gastric tumor had gastric, pancreatic, and cecal metastases. Histologically, the tumors were sharply demarcated and composed of spindle cells arranged in bundles, intermixed with small amounts of collagenous stroma. The tumor cells had mild atypia with few mitotic figures (0-5/50 high power fields, 7.95 mm2) and were immunolabeled for KIT and Discovered-on-GIST 1 (DOG1). All cases had mutations in exon 11 of the Kit gene. These findings indicate that GISTs in guinea pigs are similar to those in humans and dogs. GISTs in guinea pigs are potentially malignant submucosal tumors with KIT- and DOG1-immunolabeling, exon 11 KIT mutations, and the possibility of metastasis.

Testicular gonadoblastoma in two pet domestic rabbits (Oryctolagus cuniculus domesticus).

Testicular gonadoblastoma is an uncommon tumor in domestic animals. The current study describes a testicular gonadoblastoma in 2 pet domestic rabbits (Oryctolagus cuniculus domesticus) based on the histomorphological, immunohistochemical, and ultrastructural characteristics of the tumor. The tumor tissue consisted of discrete tubular structures separated by a fibrous stroma. The tubular structures were composed of large round cells similar in appearance to germ cells in the seminiferous tubules, and small spindle cells with oval or elongated nuclei resembling Sertoli cells. The spindle cells showed peculiar structural patterns arranged in a coronal or follicular pattern, often forming Call-Exner bodies like those in an ovarian granulosa cell tumor. One case was concomitant with seminoma. Immunohistochemistry revealed large round cells that were positive for c-kit and placental alkaline phosphatase, while spindle cells were positive for vimentin and Wilms tumor protein. Ultrastructurally, the spherical eosinophilic material (Call-Exner body) consisted of duplicated basal lamina, and sex cord components surrounded a single degenerative cell similar to a germ cell.