Acinar cell carcinoma of the pancreas: clinical and cytomorphologic characteristics

Abstract

Acinar cell carcinoma is a rare malignant epithelial neoplasm with predominantly exocrine acinar differentiation and is seen primarily in older men (mean age, 62 years). The presenting symptoms are usually non-specific, and jaundice is often not present. Symptoms relating to the overproduction and release of lipase into the circulation are present in 10-15% of patients. Characteristic cytomorphologic features include a population of cells with minimal pleomorphism, eccentrically placed nuclei with a single prominent nucleoli and moderate hyperchromasia. The cytoplasm is finely granular, and the background may contain granular debris secondary to cytolysis. A significant proportion of the cases also have a minor neuroendocrine component or scattered neuroendocrine cells. Approximately 50% of patients have metastatic disease at presentation, often restricted to the regional lymph nodes and liver. The prognosis is poor, only slightly better than that of pancreatic ductal adenocarcinoma.

Keywords: Carcinoma, acinar cell; Pancreas.

Fig. 1

Acinar cell carcinoma (ACC). ACCs are typically large (10 cm), fairly well-circumscribed, soft and fleshy. Less commonly, they can be fibrotic or form cystic masses. Other pancreatic neoplasms that form fleshy masses include well-differentiated pancreatic neuroendocrine tumor, pancreatoblastoma, solid-pseudopapillary neoplasm, and lymphoma.

Fig. 2

Acinar cell carcinoma. Neoplastic cells show acinar formations, relative cellular monotony, and foci of necrosis. Thin bands of fibrosis separate islands of neoplastic cells.

Fig. 3

Acinar cell carcinoma. Poorly differentiated neoplastic cells with focal acinar formations, large nuclei exhibiting irregular chromatin clumping, size variation, and varying N/C ratios. Many mitotic figures are present, consistent with aggressive growth.

Fig. 4

Acinar cell carcinoma. Partially intact tissue fragment with neoplastic cells has moderately hyperchromatic, uniform nuclei and delicate basophilic cytoplasm. A lack of single dispersed cells may help to differentiate this from a pancreatic neuroendocrine tumor (Diff-Quik stain).

Fig. 5

Acinar cell carcinoma. Single cells with round to ovoid, centrally- or eccentrically-located nuclei. Some of the neoplastic cells contain entangled cord-like clear areas of unknown significance. A well-differentiated endocrine neoplasm is often a difficult diagnosis to exclude, and all such cases should be immunolabeled before a definitive diagnosis is made (Diff-Quik stain).

Fig. 6

Acinar cell carcinoma. Neoplastic cells arranged singly or in groups. There are round to ovoid nuclei with uniform chromatin patterns and delicate, fragile cytoplasm. While these features are typical of acinar cell carcinomas, they may also be present in some well-differentiated pancreatic neuroendocrine tumors (Papanicolaou stain).

Fig. 7

Acinar cell carcinoma (ACC). Poorly differentiated ACC. Neoplastic cells are disorganized, but several atypical acinar formations are present. The acinar formations can be easily confused with "rosettes" of an endocrine neoplasm (Papanicolaou stain).

Fig. 8

Acinar cell carcinoma. Poorly differentiated neoplastic cells with bizarre, pleomorphic nuclei, macronucleoli, and eosinophilic cytoplasm are observed. Several well-formed intranuclear pseudoinclusions are present. The smear background is characteristically granular.