Metastatic neuroendocrine carcinoma in a dog.
Neuroendocrine carcinomas are rather rarely reported neoplastic condition among domestic animal species, especially in dogs. They originate from neuroendocrine cells, which are modified post-ganglionic neurons and are widely distributed among various organ systems of the body. Here we present a case report of metastatic neuroendocrine carcinoma in an eight year old, male German Shepherd dog that was euthanized and submitted for necropsy examination. Grossly, a large multi-nodular tumour mass involving the intestines, pancreas, mesentery and mesenteric lymph nodes was observed. Liver showed multiple creamy white areas on all the lobes with a central depression. Small, nodular foci were also seen on peritoneal and pleural linings. Histopathological examination revealed proliferation of neoplastic cells in trabecular, solid and alveolar patterns amidst variable connective tissue stroma, with eosinophilic cytoplasm and round nucleus. These cells were found to contain dark argyrophilic granules within their cytoplasm upon modified Grimelius silver staining, confirming their neuroendocrine origin. Invasions of tumour cells into the adjacent parenchyma and formation of embolism into blood vessels and lymphatics were indicative of metastatic potential. Similar histological lesions were observed in other visceral organs also. Since, the primary organ of tumour initiation could not be ascertained, the present case was diagnosed as metastasising neuroendocrine carcinoma of unidentified origin.