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Exocrine Pancreatic Tumours.

Recent immunohistochemical re-evaluation

(Cubilla & Fitzgerald) revealed that microglandular

 adenocarcinoma does not constitute an entity of its

own, but comprises a group of tumours with heterogeneous

histologic features and immunostaining patterns.

These tumours should be classified with ductal

 adenocarcinoma having neuroendocrine,

acinar or mixed immunohistochemical phenotype.

The main importance of recognizing this rare variant of

pancreatic adenocarcinoma lies in avoiding

misdiagnosis with other primary and  metastatic

 neuroendocrine neoplasms of this organ.

Immunohistochemical and ultrastructural examination will

be of value in such cases for differential diagnosis.

The term microadenocarcinoma was first proposed for a subtype of pancreatic carcinoma by Cubilla and Fitzgerald in 1975 based largely on the morphological features of 15 cases. Since that time, no independent studies have appeared in the English literature to address whether microadenocarcinoma represents a distinctive tumor or a pattern of growth, and some authors have questioned its existence as a definable entity. Immunohisto-chemistry is now available to allow the identification of lines of differentiation in pancreatic neoplasms, on which their classification is largely based. Reasoning that heterogeneity of differentiation between different cases would not justify the separation of microadenocarcinomas from other better defined pancreatic neoplasms, we reevaluated 12 cases from the original series using antibodies for acinar, endocrine, and ductal differ-entiation. Two distinctive morphological patterns were identified: microglandular and solid cribriform. The microglandular cases (n = 6) were not separable from typical ductal adenocarcinomas either morphologically or immunophenotypically. Of the solid-cribriform cases (n = 6), immunohistochemistry revealed three to be acinar cell carcinomas, one an endocrine carcinoma, one a mixed endocrine-ductal carcinoma, and one a ductal adenocarcinoma. We concluded that with the benefit of further study, most of these cases could be reclassified as other types of pancreatic carcinoma. Microadenocarcinoma is best regarded as a pattern of growth associated with an aggressive clinical course rather than a distinctive entity.

Microglandular carcinoma of the pancreas: immunohistochemical and ultrastructural study of an unusual variant of pancreatic carcinoma that may closely resemble a neuroendocrine neoplasm. Am J Clin Pathol. 1996 Jun;105(6):727-32.

Two cases are described of an unusual form of primary adenocarcinoma of the pancreas characterized histologically by their striking resemblance with a neuroendocrine neoplasm. The tumors were composed of a population of relatively small, uniform cells arranged in sheets admixed with small microglandular structures resulting in a cribriform pattern of growth. The tumor cells displayed scant cytoplasm with indistinct cell borders and round to oval nuclei with irregular clumping of chromatin and small, inconspicuous nucleoli. Immunohistochemical studies in both cases showed positivity of the neoplastic cells with CAM 5.2 antibodies and negative staining with a battery of neuroendocrine-related markers including chromogranin, NSE and synaptophysin, as well as with a variety of peptide hormones including insulin, glucagon, vasoactive intestinal polypeptide, gastrin and serotonin. Ultrastructural examination revealed a cohesive population of cells forming abortive glandular lumens lined by imperfectly formed microvilli and showing well-developed junctional complexes. No dense core neurosecretory granules or zymogen granules could be identified in any of the cells, supporting a ductal type of differentiation for these tumors. The main importance of recognizing this rare variant of pancreatic adenocarcinoma lies in avoiding misdiagnosis with other primary and metastatic neuroendocrine neoplasms of this organ. Immunohistochemical and ultrastructural examination will be of value in such cases for differential diagnosis.

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