Solid and cystic acinar cell tumors of the pancreas. A report of two cases with immunohistochemical and ultrastructural studies.

Two pancreatic tumors were found in young women without detectable functional symptoms. These tumors were identical in gross, histological and electron microscopic features. Each of them formed a large abdominal mass. One of them was found because of this abdominal mass, while the other was found incidentally. Grossly, the tumors were well circumscribed by a firm, white, fibrous capsule, and their cut-surfaces showed mainly cystic degenerative changes with necrotic and hemorrhagic material, with only some solid portions. The solid portions were composed of uniform cells forming solid and papillary structures with numerous PAS-positive diastase-resistant granules. Immunohistochemical staining for alpha 1-antitrypsin showed a granular distribution. Electron microscopic examination showed that the tumor cells had numerous mitochondria, zymogen-like granules, and annulate lamellae. These findings strongly suggested acinar cell differentiation, although ductal and endocrine differentiation have also been observed by others. Therefore, this type of tumor can best be termed an acinar cell tumor. There was no recurrence in either patient after the operation. Long survival can be expected, but reports indicate that this neoplasm should be recognized as a lesion of low malignancy.