Case 170317-2

Nine-year-old, castrated, male dog (Jack Russell terrier)

This animal was originally presented for a ten-day history of anorexia and lethargy. Abdominal ultrasound indicated gastritis with limited motility and focal ulceration. An endoscopic biopsy of the stomach was submitted for review.

No significant lesions. Only pinch biopsy samples were submitted.

Ten small sections of stomach are examined in which the lamina propria contains multifocal regions of hemorrhage. Dissecting through normal glandular structures within the lamina propria of multiple sections, An epithelial population that forms variably-sized, irregularly-spaced acini and tubules dissects through the superficial lamina propria, separating normal gastric glands. The infiltrating cells have moderate to marked anisocytosis and anisokaryosis. The tubules and acini are often lined by multiple layers of epithelium and contain light basophilic, whispy material (possibly mucin). In one sample, the mucosa is replaced by sheets of dysplastic epithelial cells that rarely form acini or tubules. Many cells in this population have abundant, lightly basophilic vacuolar cytoplasm suggestive of mucin and, in some, large vacuoles marginalize the chromatin. Cell margins are sometimes indistinct. Nuclei are typically large and multinucleate cells are scattered throughout. Most nuclei are round to oval, but some are elongate or clefted. Chromatin is lightly granular to vesicular, and there is usually a single large nucleolus. Mitotic figures are rare, and there are scattered apoptotic cells. A small to moderate number of lymphocytes and plasma cells are scattered throughout the sections and occasionally form aggregates in the mucosa. Other samples contain small regions of hemorrhage in the mucosa.

The infiltrating cell population was intensely stained by a pan-cytokeratin immunohistochemical assay.

Stomach: Adenocarcinoma

The dysplastic, hyperplastic population in the stomach was thought to be consistent with an adenocarcinoma. However, the nearly diffuse infiltration of the lamina propria and no chance of observing deeper invasion in the superficial samples, made this diagnosis less obvious than in some similar cases. Pseudo-carcinomatous hyperplasia secondary to mucosal necrosis or ulceration was one rule-out that was considered.

The animal was monitored on supportive care for a few more days but continued to decline. The owners opted for euthanasia, and a necropsy was performed. A small ulcer was present in the body of the stomach but there was no mass-like effect or cicatricial scarring of the gastric wall to suggest a carcinoma might be present. Nonetheless, histopathology revealed an invasive, often mucinous carcinoma that extended through the full thickness of the tunica muscularis. An immunohistochemistry stain for cytokeratins (pancytokeratin) revealed large numbers of neoplastic epithelial cells in the deep tissues of the stomach, which were not evident by examination of the HE-stained sections.