Spontaneous gastric carcinoid tumors in the striped field mouse (Apodemus agrarius)

Gastric carcinoid tumors were found in seven of 135 striped field mice (Apodemus agrarius) by routine histopathologic examination. All these carcinoids occurred in mature striped field mice aged 72-100 weeks. Six animals were females and only one was male. Only two of seven tumors were detectable by gross examination. Grossly, tumors were located in the fundus of the glandular stomach. All seven tumors were microscopically single in the stomach and two mice exhibited extragastric metastasis. Tumors from all the mice were characterized by densely packed sheets of round to polygonal cells, subdivided into packets by a fine fibrovascular stroma. The cytoplasm of all tumor cells from all the mice contained argyrophil granules when stained by Grimelius and Sevier-Munger silver procedures. All seven mice with gastric carcinoids exhibited positive immunoreactivity to neuron specific enolase. Psammoma bodies, concentrically laminated microcalcification, were characteristic findings in gastric carcinoids from five mice. There were also a concomitant and independent hepatocellular adenoma in one case and hepatocellular carcinoma in two cases. The present cases provide the first description of spontaneous gastric carcinoid tumors in the striped field mice.