Fibrillary inclusions in neoplastic and fetal acinar cells of the pancreas

Abstract

We report a case of pancreatic acinar cell carcinoma which contained a large number of pleomorphic inclusions with fibrillary internal structures and mature zymogen granules. To clarify the significance of fibrillary inclusions in the differentiation of acinar cells of the pancreas, we further investigated fetal pancreases (gestational weeks 16, 17, 19, 20 and 28). We found two types of inclusions: type A, corresponding to fibrillary inclusion of neoplastic acinar cells, was observed only 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 after the 17th gestational week. Although the type A inclusion might be generated through a different mechanism than the type B inclusion, the appearance of a large number of fibrillary inclusions in neoplastic acinar cells may represent a transient form of zymogen granule.

Loss of CAPS2/Cadps2 leads to exocrine pancreatic cell injury and intracellular accumulation of secretory granules in mice

“…The filamentous granules in Cadps2 KO acinar cells correspond well to those which are generally known to be a characteristic of acinar cell carcinomas; both categories of granules display variously-elongated shapes and rich filaments bound in limiting membrane (for a review see ( Chong et al, 1996 )). These granules can transform into secretory granules, as indicated by the presence of their morphological intermediates in tumor tissues ( Ordóñez and Mackay, 2000 ) and by transient appearance of the former, elongated granules in a certain phase of fetal development ( Chong et al, 1996 ). The present study is the first demonstration of the filamentous granules in non-cancerous, mature acinar cells.…”

Acinar cell carcinoma of the pancreas showing finger-print-like zymogen granules by electron microscopy: immunohistochemical study

“…Hence, a firm diagnosis has always hinged on electron microscopy and immunohistochemistry. The ultrastructure of malignant acinar cells is characterized by the presence of large zymogen granules (>500 nm) and, in some cases, by a large number of pleomorphic, membrane‐bound inclusions with fibrillary internal structures that may represent a transient or deranged form of zymogen granules 10,18,19. In our patient, the tumor cells contained characteristic zymogen‐like granules with finger‐printlike patterns.…”

“…Surgical resection provides the only hope of cure in the few patients who present with local disease without metastases 28. However, since these tumors have a better prognosis than ductal carcinoma,9 a more aggressive approach, with combined pancreatic and hepatic resection, has been suggested in patients with a limited number of liver metastases 18. Few patients appear to respond to chemotherapy 13,29,30…”

Brush cytology of acinar cell carcinoma of the pancreas with intraductal growth

“…Ultrastructurally, ACCs often contain numerous large cytoplasmic granules, known as zymogen granules, and filamentous inclusions that are thought to lie within the spectrum of zymogen granules . These inclusions are present in primary pancreatic tumors, particularly pure ACC, but less frequently in mixed acinar‐endocrine carcinoma.…”