Metastatic gastric adenocarcinoma in a grey seal Halichoerus grypus: clinicopathological and immunohistochemical characterization.

A 33 yr old female grey seal Halichoerus grypus presented with inappetence and progressive weight loss. Medical management included blood analysis, imaging, and fecal evaluation, along with multimodal supportive therapy, which periodically improved the overall medical condition. Six months after the initial presentation, the clinical condition deteriorated significantly, including severe hyporexia, hematemesis, and marked neutrophilic leukocytosis, which led to the decision to euthanise based on welfare grounds. Necropsy findings included severe thickening of the distal esophagus, cardia, and proximal gastric fundus, as well as multiple nodular to cystic structures over the stomach's serosa, omentum, and mesentery. Histologically, a mucinous gastric adenocarcinoma was diagnosed, with metastasis to the gastric lymph nodes and prominent carcinomatosis involving the omentum, mesentery, and diaphragm. Immunohistochemically, the gastric adenocarcinoma was positive for cytokeratin AE1/AE3, weakly positive for COX-2 and E-cadherin, and negative for vimentin. The Ki-67 proliferative index was low (0.8). Although rare, this case offers further insights into the clinical presentation, histopathology, and immunohistochemical profile of gastric tumors in pinnipeds.