Pancreatic serous microcystic adenoma with extensive oncocytic change.

Herein is reported a case of pancreatic serous microcystic adenoma with extensive oncocytic change in a 73-year-old woman. Histologically the tumor consisted of numerous small cysts, separated by thin or broad fibrous septa. These cysts were lined with uniform cells having abundant eosinophilic granular cytoplasm, which was negatively or weakly stained with PAS. Immunohistochemically, the cyst-lining cells were positive for cytokeratin (CK) 7, CK19, MUC1, MUC6, alpha-inhibin, and neuron-specific enolase (NSE), and negative for CK8, CK20, MUC2, and MUC5AC; these immunoprofiles coincide with those of serous microcystic adenoma. Immunostaining with anti-mitochondrial antibody showed dense granular positivity in the cytoplasm, which suggested an oncocytic phenotype. Thus, this case is considered a variant of serous microcystic adenoma characterized by extensive oncocytic change. To the authors' knowledge no similar case has been reported in the literature. It may pose problems in the differential diagnosis of the cystic pancreatic tumors with oncocytic change, but can be diagnosed on histology and immunohistochemistry.