FIBRILLARY INCLUSIONS IN NEOPLASTIC AND FETAL ACINAR-CELLS OF THE PANCREAS

We report a case of pancreatic acinar cell carcinoma which contained a large number of pleomorphic inclusions with fibrillary internal struc tures and mature zymogen granules. To clarify the significance of fibr illary inclusions in the differentiation of acinar cells of the pancre as, we further investigated fetal pancreases (gestational weeks 16, 17 , 19, 20 and 28). We found two types of inclusions: type A, correspond ing to fibrillary inclusion of neoplastic acinar cells, was observed o nly in a 19-week fetus; type B showed a homogeneous density similar to that of zymogen granules. Type B was observed in all the fetuses afte r the 17th gestational week. Although the type A inclusion might be ge nerated throught a different mechanism than the type B inclusion, the appearance of a large number of fibrillary inclusions in neoplastic ac inar cells may represent a transient form of zymogen granule.