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Acinar Cell Cystadenoma of the Pancreas: A Benign Neoplasm or Non-Neoplastic Ballooning of Acinar and Ductal Epithelium?

Singhi, Aatur D. MD, PhD*; Norwood, Stephanie MD; Liu, Ta-Chiang MD, PhD; Sharma, Rajni PhD; Wolfgang, Christopher L. MD, PhD‡,§; Schulick, Richard D. MD‡,§; Zeh, Herbert J. MD; Hruban, Ralph H. MD†,‡

American Journal of Surgical Pathology: September 2013 - Volume 37 - Issue 9 - p 1329–1335
doi: 10.1097/PAS.0b013e3182a1ad72
Original Articles

Acinar cell cystadenoma (ACA) of the pancreas was initially described as a non-neoplastic cyst of the pancreas and, at that time, referred to as “acinar cystic transformation.” In subsequent studies, these lesions were given the designation of “-oma,” despite the relative lack of evidence supporting a neoplastic process. To characterize these lesions further, we examined the clinical, pathologic, and immunohistochemical features of 8 ACAs. The majority of patients were female (7 of 8, 88%) and ranged in age from 18 to 57 years (mean, 43 y). Grossly, the cysts involved the head (n=5), body (n=1), or the entire pancreas (n=2). ACAs were either multilocular (n=4) or unilocular (n=4) and ranged in size from 1.8 to 15 cm (mean, 6.8 cm). Histologically, multilocular ACAs were lined by patches of acinar and ductal epithelium. Immunolabeling, including double-labeling for cytokeratin 19 and chymotrypsin, highlighted the patchy pattern of the ductal and acinar cells lining the cysts. In some areas, the cysts with patches of acinar and ductal differentiation formed larger locules with incomplete septa as they appeared to fuse with other cysts. In contrast, the unilocular cases were lined by 1 to 2 cell layers of acinar cells with little intervening ductal epithelium. Nuclear atypia, mitotic figures, necrosis, infiltrative growth, and associated invasive carcinoma were absent in all cases. In addition, we assessed the clonal versus polyclonal nature of ACAs, occurring in women, using X-chromosome inactivation analysis of the human androgen receptor (AR) gene. Five of 7 cases were informative and demonstrated a random X-chromosome inactivation pattern. Clinical follow-up information was available for all patients, and follow-up ranged from 10 months to 7.8 years (mean, 3.6 y), with no evidence of recurrence or malignant transformation. We hypothesize that early lesions are marked by acinar dilatation that expands into and incorporates smaller ductules and later larger ducts. As the cysts increase in size, they fuse forming larger cysts. Later lesions demonstrate a unilocular cyst lined by predominantly acinar epithelium with scattered ductal cells. The term cystadenoma, with its neoplastic connotation, does not seem to accurately reflect the histologic, immunohistochemical, or molecular features of these lesions. We suggest readopting the term “acinar cystic transformation” until the non-neoplastic versus neoplastic origin of these lesions can be resolved.

Departments of *Pathology

Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA

Departments of Pathology

Oncology

§Surgery, The Sol Goldman Pancreatic Cancer Research Center, Johns Hopkins University School of Medicine, Baltimore, MD

Present address: Ta-Chiang Liu, MD, PhD, Department of Pathology and Immunology, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8118, Saint Louis, MO 63110.

Conflicts of Interest and Source of Funding: Supported in part by a grant from the National Pancreas Foundation, Western Pennsylvania Chapter (to A.D.S.). The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article.

Correspondence: Ralph H. Hruban, MD, The Johns Hopkins Medical Institutions, 401 N. Broadway, Weinberg 2242, Baltimore, MD 21231-2410 (e-mail: rhruban@jhmi.edu).

© 2013 by Lippincott Williams & Wilkins.