Acinar Cell Carcinoma of the Pancreas

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Acinar Cell Carcinoma of the Pancreas

Acinar cell carcinoma of the pancreas, also acinar cell carcinoma, is a rare malignant exocrine tumor of the pancreas. It represents 5% of all exocrine tumors of the pancreas, making it the second most common type of pancreatic cancer. It is abbreviated ACC.  Acinar cell carcinoma of the pancreas is a rare neoplasm, comprising 1-2 % of exocrine pancreatic tumors (Solcia 7). The tumor most commonly occurs in middle-aged or elderly Caucasian men.

Patients may present with vague abdominal pain, or the mass may be found incidentally. Patients (up to 15%) can also present with widespread subcutaneous fat necrosis, polyarthritis, and eosinophilia (Schmidt’s triad) due to increased circulating lipase secreted by the tumor (Solcia, Ashley and Lauwers 22). Acinar cell carcinomas can involve the head or tail of the pancreas. They are usually well circumscribed, partly encapsulated, pink to tan, homogeneous fleshy mass, averaging 11 cm in greatest diameter, occasionally demonstrating extensive hemorrhage and necrosis (Klimstra DS 92). Microscopically, most tumors are highly cellular with minimal stroma and lack the stromal desmoplasia commonly seen with ductal adenocarcinomas. Four patterns of growth have been described (Klimstra DS.)

The disease is more common in men than women are and the average age at diagnosis is about 60. Symptoms are often non- specific and include weight loss. A classic presentation, found in around 15% of cases includes subcutaneous nodules (due to fat necrosis) and arthralgias, caused by release of lipase. The change in exocrine mass is an important parameter to follow in experimental models of pancreatic injury and regeneration. However, at present, the quantitative assessment of exocrine content by histology is tedious and operator-dependent, requiring manual assessment of acinar area on serial pancreatic sections. In this study, we utilized a novel computer-generated learning algorithm to construct an accurate and rapid method of quantifying Acinar content.

The algorithm works by learning differences in pixel characteristics from input examples provided by human experts. HE-stained pancreatic sections were obtained in mice recovering from a 2-day, hourly caerulein hyperstimulation model of experimental pancreatitis. For training data, a pathologist carefully outlined discrete regions of Acinar and non-Acinar tissue in 21 sections at various stages of pancreatic injury and recovery termed the “ground truth”. After the expert defined the ground truth, the computer was able to develop a prediction rule that was then applied to a unique set of high- resolution images in order to validate the process. For baseline, non- injured pancreatic sections, the software demonstrated close agreement with the ground truth in identifying baseline Acinar tissue area with only a difference of 1%±0.05% (p = 0.21

The Acinar pattern is present in most tumors, often admixed with trabecular and glandular patterns; the solid pattern is also often seen. The tumor cells resemble normal pancreatic acinar cells. The nuclei are round to oval, with only mild pleomorphism and single prominent nucleoli. The cytoplasm tends to be abundant, eosinophilic, and granular due to zymogen granules, which are PAS-positive and diastase-resistant, but in the solid tumors, PAS positivity may be scant. Mitotic activity is variable, form rare mitoses to >50 per 10 HPF. In the present case, the differential diagnosis, based on morphology, included an acinar cell carcinoma and a pancreatic endocrine tumor because the pattern of growth was mostly solid with rare areas of acinar type structures. However, the lack of classic “salt and pepper” chromatin distribution and the presence of prominent single nucleoli are unusual for endocrine neoplasms.

Since normal pancreatic acinar cells secrete pancreatic enzymes, the most useful histochemical and/or immunohistochemical stains for acinar cell carcinoma are for the pancreatic enzymes, such as trypsin, chymotrypsin, amylase, elastase, and lipase. When the neoplastic cells exhibit nuclear polarity, these stains usually demonstrate positivity in the apical portions of the cells, while the stains are more focal and usually restricted to single cells in tumors with solid patterns. Tumor cells that are positive for synaptophysin and chromogranin A can be found in 30-50% of cases (Notohara 20).

Usually they occur in tumors with a solid pattern, where they are scattered throughout the tissue. Although only a small number of cases with synaptophysin immunohistochemistry have been reported, the diffuse positi.............