Answer to “What’s Your Diagnosis?”

Diagnosis: Pancreatic mixed acinar-islet cell adenoma.

Discussion:

The pictures are of two cases of mixed acinar-islet cell adenoma in the F344/N rat. The acinar and islet cells are intermingled and occasional mitoses are present in both cell populations.

Pancreatic mixed acinar-islet cell adenomas are rare neoplasms of rats and mice, and have been documented in other species. The background incidence of this tumor for F344/N rats receiving the NTP 2000 diet is 0.3% in males and 0% in females. They are behaviorally benign tumors seen as discrete, solitary and well-circumscribed nodules, with a bimorphic population of well-differentiated neoplastic islet and acinar cells. Both cell types are increased in number.

In man, these tumors are malignant and mixed acinar-exocrine carcinomas are diagnosed when at least one-third of the neoplasm is composed of exocrine or endocrine cells. The two cell populations are intermixed and may contain cells with intermediate differentiation (amphicrine features). Embryologically, pancreatic acini and islets have a common origin, arising from intralobular ductal cells.

References:

• Riley M, Boorman G, and Hayashi Y: in Pathology of the Fischer rat. Academic Press, Inc. San Diego, New York, Boston, London, Sydney, Tokyo, Toronto. Boorman GA, Eustis SL, Elwell MR, Montgomery CA, Jr, MacKenzie WF,eds. (1990); p545-553
• AFIP, Atlas of Tumor Pathology, Tumors of the pancreas, 3rd series Fascicle 20 (1997) p112

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