This report presents a case of two smooth muscle hamartomas of the stomach in a 10-year-old male Boxer. The clinical history of the animal was of chronic vomiting, weight loss, and intermittent gastric distension, and it died because of chronic and congestive heart failure. Gross, histology, and immunohistochemistry (IHC) exams were performed. On necropsy, in the pyloric region of the stomach, two closely related polypoid growths between 10 and 15？mm in diameter were identified. On the cut sections, both polyps presented white to gray color, with homogenous architecture and well-defined limits. The thickness of the submucosal layer was seen to be increased to 1？cm. No other gastric alterations were identified by the necropsy exam. Histologically, both masses growth consisted of hyperplastic glands lined by foveolar epithelium, arranged in a papillary or branching pattern, and supported by a core of well-vascularised and marked smooth muscle tissue interspersed between glands. No dysplastic cells and mitotic figures were observed in these lesions. Immunohistochemistry revealed a strong cytoplasm labelling for smooth muscle actin of the bundles around the mucosal glands. To our knowledge, this is the first report of smooth muscle hamartomas mimicking multiple gastric polyps in dogs. 1. Introduction Gastric polyps (GP) are sessile or pedunculated growths that arise from the mucosa and protrude into the gastric lumen as the result of either hyperplasia or neoplasia [1]. GP occur sporadic in dogs [2, 3], cats [4], cattle [5], and horses [6]; they are observed during gastric endoscopy or necropsy. GP are often in the pyloric region, and the affected animals usually do not show any clinical signs however. GP can produce vomiting after food intake, weight loss, and bleeding when these lesions reach a considerable size and rarely cause pyloric stenosis [2, 3]. Macroscopically, GP are described as solitary or multiple bulging sessile or pedunculated formations, with an irregular and arborescent surface [7]. In human pathology, various types of nonneoplastic gastric polyps, including hyperplastic, inflammatory fibroid, xanthoma, hamartomatous of the Peutz-Jeghers type, juvenile, gastric polyps in Cowden disease, and gastric polyps in Cronkhite-Canada syndrome, are described [8]. In domestic animals, there is a lack of data about the histological features of the gastric polyps. Based on histological findings, two gastric polyps have been distinguished: hyperplastic and inflammatory (benign lymphoid) [1]. The pathogenesis of development of the GP in dogs is still
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