A case of papillary cystic tumor (PCT) of the pancreas in a 55-year-old woman is described. She presented with a gradually enlarging and painless abdominal mass for >26 years. The tumor was encapsulated and measured 16 × 12 × 10 cm. The gross features and conventional light microscopic appearances of this tumor were consistent with the previously reported cases of PCT. Perineural and capsular invasions were found. In addition to the densely packed blue granules in the cytoplasm demonstrated by phosphotungstic acid-hematoxylin stain, ultrastructural study revealed the tumor cells to be packed with numerous mitochondria. These oncocytes comprised almost all the non-necrotic tumor areas. Therefore, this case was indistinguishable pathologically from oncocytic carcinoma of the pancreas. DNA flow cytometry showed a diploid pattern and low S phase fraction, indicating that the tumor has a low proliferative activity and a favorable prognosis.
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