Pancreatic Acinar Cell Carcinoma

Eric Richard Handley, MD - Case Coordinator
Matthew P Schenker, MD - Radiology Discussion
Priscilla S Chang, MD, PhD - Pathology Discussion
Steven E Seltzer, MD - Attending Radiologist

January 26, 2004

Presentation

Imaging Findings

Post-contrast axial CT images show a heterogeneous mass abutting the head of the pancreas and the gastric entrance to the duodenum. There are areas of lower density, suggesting cystic degeneration or fluid attenuation, and punctate calcifications. Neither the common duct nor the pancreatic duct appears to be dilated. Other solid organs appear to be normal. The location (stomach, pancreas, duodenum, or other) is not clear. The coronal reformat does not clarify the origin, but does indicate that the mass hugs the base of the liver. Only the periphery of the duodenum is visible on these images.

Differential Diagnosis

Diagnosis

Discussion

The gross specimen, resulting from a Whipple resection, includes a 4-cm, well-encapsulated mass in the anterior pancreatic head. The lesion is firm and has a white, nodular appearance. The cut section shows areas of cystic degeneration, necrosis, and hemorrhage. Low-power microscopy reveals solid, uniform sheets of cells. The appearance is monotonous. At higher power, abundant pink, eosinophilic cytoplasm (with granules) is visible. The nuclei are not highly pleomorphic. This appearance is characteristic of acinar cell carcinoma; the diagnosis was confirmed by PAS-D staining, which highlighted cytoplasmic granules in tumor cells, and by immunohistochemical staining, which verified the presence of a1-antichymotrypsin.

Radiology Discussion

Pancreatic tumors are categorized as exocrine and endocrine. Each of these categories is further divided; exocrine tumors can be solid or cystic, while endocrine tumors may be functional or non-functional. Acinar cell carcinoma is a solid epithelial exocrine tumor.

The pancreas is composed predominantly of acinar cells (82%). Even so, acinar cell carcinoma accounts for only 1% of all primary pancreatic neoplasms. Acinar cell carcinomas are active exocrine tumors. They occur more commonly in men and show a peak of incidence in the seventh decade. These tumors are lower grade than ductal carcinoma, although they are usually advanced at presentation. They tend to be large (mean size ~10 cm), locally invasive, and usually metastatic (especially to liver) at the time of diagnosis. Clinical symptoms include nonspecific gastrointestinal symptoms; the initial presentation may be similar to that of ductal adenocarcinoma of the pancreas. Patients often, however, display a unique paraneoplastic syndrome characterized by increased serum lipase, lobular panniculitis (mimicing erythema nodosum), and polyarthritis. The panniculitis and arthritis are, presumably, the result of lipase-digested adipose tissue. On CT, acinar cell tumors are hypodense with occasional calcifications, a central necrotic area, and a well-defined, enhancing wall. These tumors are slightly hypointense on T1-weighted MRI and hyperintense T2-weighted images. They demonstrate poor enhancement after gadolinium injection due to relative hypovascularity compared to pancreatic parenchyma.

As a comparison, ductal adenocarcinoma represents 90-95% of primary pancreatic neoplasms and is the fifth leading cause of cancer mortality in U.S.; the 1-yr mean survival rate is just 8%. Its incidence increases with age (65% > 60 yr); 30% of known cases are associated with a history of smoking (relative risk 2-3). Other risk factors include obesity, long-standing diabetes (RR 2), chronic pancreatitis (RR 26), hereditary (RR 50). Like acinar cell carcinoma, ductal adenocarcinoma is more common in men (1.2-1.5:1). Clinical symptoms include pain and weight loss (75%), jaundice (>80% of pancreatic head lesions), Courvoisier’s sign (palpably enlarged, non-tender gallbladder; 25% of pancreatic head lesions), glucose intolerance, venous thrombosis and migratory thrombophlebitis (Trousseau’s syndrome).

The majority of ductal adenocarcinomas (70%) arise in the head of the pancreas; just 5-10% of these are curable. The remainder occur in the body and tail of the pancreas and are incurable. Enlargement of the pancreas may be subtle. Unenhanced abdominal CT is only 70-80% sensitive; 40-50% of tumors smaller than 3 cm are missed. The sensitivity of ultrasound, however, is even lower. Dual-phase contrast enhancement significantly improves the sensitivity and specificity of CT.Ductal adenocarcinomas are hypodense on CT because of edema and necrosis. Calcifications are extremely uncommon (in contrast to acinar, cystic and islet cell tumors). These masses commonly cause obstruction of the common bile duct and pancreatic duct when located in the pancreatic head (so-called “double duct” sign), but masses in the uncinate process may not cause obstruction.

Two other entities in the differential diagnosis for a mass in the head of the pancreas are pancreatoblastoma and anaplastic carcinoma. Pancreatoblastoma is a rare, primitive neoplasm of childhood (ages 1-8 yr) that has been reported occasionally in neonates and adults. It is slightly more common in boys than girls. The congenital form is associated with Beckwith-Wiedemann syndrome. The clinical presentation typically includes a palpable mass with a soft and gelatinous consistency, rarely resulting in obstructive symptoms. On CT, these are large, well-defined, multilobulated masses with enhancing septa and areas of necrosis. On ultrasound, they demonsrate mixed echotexture. Anaplastic carcinomas are rare tumors that display a variety of growth patterns. The literature lacks a comprehensive study of this tumor. They are typically large at presentation, and clinical symptoms are vague (weight loss, pain, and fatigue, nausea, or vomiting). Anaplastic carcinomas typically arise in the head or tail of the pancreas and are widely infiltrative; histologically, they are separated into large, pleomorphic or spindle cell groups. Patients with K-ras mutations have a shorter survival time, but overall prognosis for all anaplastic carcinomas is dismal (average survival, 448 days).

References

Klimstra DS, Heffes CS, Oertl J, Rosai J. Acinar cell carcinoma of the pancreas. A clinicopathologic study of 28 cases. Am J Surg Pathol 1992; 16:815-37.

Klimstra DS, Wenig BM, Adair CF, Heffess CS. Pancreatoblastoma, A clinicopathologic study and review of the literature. Amer J Surg Pathol 1995; 19(12):1371-1389.

Longnecker DS, Shinozuka H, Deker A. Focal acinar cell dysplasia in human pancreas. Cancer 1980; 45:530-540.

Mergo PJ, Helmberger TK, Buetow PC, Helmberger RC, Ros PR. Pancreatic neoplasms: MR imaging and pathologic correlation. Radiographics 1997; 17: 281-301.

Paal E, Thompson LD, Frommelt RA, Przygodzki RM et al. A clinicopathologic and immunohistochemical study of 35 anaplastic carcinomas of the pancreas with a review of the literature. Ann Diagn Pathol 2001; 5:129-140.

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