A canine insulinoma with amphicrine differentiation: morphological and immunohistochemical characteristics.

A 10-year-old male toy poodle presented with hypoglycemia. An insulinoma was suspected and a surgical excision of two pancreatic masses was performed. White-gray, demarcated, soft masses were identified in the pancreas. Histopathologically, two types of growth patterns were observed in the same neoplasm: nest and glandular. To investigate cellular differentiation, we performed immunohistochemical and transmission electron microscopy analyses. Both types of neoplastic cells were immunopositive for INSM1, Nkx2.2 and insulin. However, the neoplastic cells exhibiting the nest pattern contained exocrine granules, whereas those with the glandular pattern were immunopositive for cytokeratin. Both types of neoplastic cells showed not only neuroendocrine but also exocrine differentiation in the same neoplastic cell. To the best of our knowledge, this is the first report describing the morphology and immunophenotype of the canine insulinoma with amphicrine differentiation: showing both neuroendocrine and exocrine features.