Chromogranin A plasma concentration and expression in pancreatic islet cell tumors of dogs and cats.

Objectives: To describe expression of the neuroendocrine marker chromogranin A (CgA) in canine and feline pancreatic islet cell tumors and their metastases, and to evaluate plasma CgA concentration in dogs and cats with insulinoma.
Sample Population: Paraffin-embedded tissues from 25 canine and 2 feline pancreatic islet cell tumors, 5 canine and 6 feline exocrine pancreatic tumors, and normal pancreatic tissue from 2 dogs and 2 cats. Heparinized plasma samples from 3 dogs and 2 cats diagnosed with insulinoma, and 10 control plasma samples from each species.
Procedure: Immunohistochemical analysis was performed on the 42 tissue specimens, using antisera against CgA, neuron-specific enolase, insulin, somatostatin, glucagon, and pancreatic polypeptide. The 25 plasma samples were evaluated, using a soluble-phase, double-antibody, equilibrium radioimmunoassay directed against the amino- and carboxy-terminal peptides of bovine CgA.
Results: Chromogranin A expression was found in 76% of canine and 2 of 2 feline pancreatic islet cell tumors. Of 7 animals with CgA immunoreactivity in primary tumors, 6 also had CgA immunostaining of metastatic lesions. Plasma CgA concentration in 2 dogs with insulinoma (0.9, 1.0 ng/ml) exceeded the reference range established for 10 clinically normal control dogs (0.50 +/- 0.16 ng/ml). Feline plasma CgA samples had extensive nonspecific background immunoreactivity.
Conclusions: Chromogranin A is a useful immunohistochemical marker for pancreatic tumors of neuroendocrine origin and their metastases. Plasma CgA concentration determined by radioimmunoassay was high in 2 dogs with insulinoma.
Clinical Relevance: Immunohistochemical staining of tissues or cytologic specimens for CgA and/or neuron-specific enolase may help distinguish masses of unknown origin as neuroendocrine in nature. Increase in plasma CgA concentration may be useful diagnostically for animals with suspected neuroendocrine tumors.