Pancreas - Acinar cell carcinoma

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Pancreas

Tumors

Acinar cell carcinoma

Reviewer: Deepali Jain, M.D. (see Reviewers page)
Revised: 24 November 2012, last major update August 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

General
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● Malignant epithelial neoplasm composed of cells with morphological resemblance to acinar cells and with evidence of pancreatic exocrine enzyme production (WHO)
● Resembles similar tumor in parotid gland
● 1-2% of pancreatic malignancies

Clinical features
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● 85% men; mean age 62 years (range, 40-81 years), rare in children (Am J Surg Pathol 1992;16:815)
● 10% have lipase hypersecretion syndrome (subcutaneous fat necrosis, polyarthralgias, occasional eosinophilia, nonbacterial thrombotic endocarditis) due to tumor lipase secretion by tumor; these patients usually have liver metastases
● Tumors may also secrete alpha-fetoprotein (AFP), and most AFP+ pancreatic neoplasms are acinar cell carcinomas or pancreatoblastoma (Hum Pathol 2000;31:938)
● 50% have metastases at diagnosis (liver and regional lymph nodes)
● 5 year survival is only 10%
● Variant with intraductal polypoid growth: less aggressive behavior, fewer metastases, smaller size (Am J Surg Pathol 2010;34:1025, Int J Surg Pathol 2011;19:795)
● Poor prognostic factors: stage III/IV versus I/II (Am J Surg Pathol 2012;36:1782)

Case reports
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● 44 year old woman with pancreatic mass (Arch Pathol Lab Med 2002;126:985)
● 50 year old man (Arch Pathol Lab Med 2001;125:1127)

Gross description
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● Well circumscribed, soft/fleshy (since minimal stroma) with fibrous septa, large (mean 11 cm), hemorrhage and necrosis common

Gross images
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Cut surface displays large nodules separated by fibrous strands, with frequently necrotic foci

Soft and circumscribed tumor with abundant hemorrhage, which projects into duodenum

Micro description
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● Note: must document pancreatic enzymes to be considered an acinar cell tumor
● Highly cellular with minimal stroma and no desmoplasia
● Solid, nesting, glandular or acinar patterns with sharp luminal space outlines
● Monotonous, uniform polarized cells with abundant eosinophilic granular apical cytoplasm due to zymogen granules (scanty in solid tumors), basal nuclei and single prominent nucleoli
● Moderate nuclear atypia, variable mitoses, no mucin
● Vascular invasion often present
● 30-50% have minor endocrine component based on immunohistochemistry
● Tumors with solid or trabecular pattern resembles endocrine tumors

Micro images
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Various images

Tumor is markedly cellular with gross lobulation by broad fibrous strands; stroma is scant within large tumor lobules

Mixture of acinar, trabecular and solid patterns

Nuclei are somewhat irregular in size; nuclei are polarized in acinar formations

Pure acinar pattern resembles normal pancreas

Dilated acini form "microglandular" structures

Round cells with scant cytoplasm, slightly irregular nuclei, distinct nucleoli

PAS: tumor cells have abundant, finely granular cytoplasm, which is PAS+ in apical portion

Trypsin stains tumor cells intensely (right side), normal acinar tissue is also typsin+ (right side)

Trypsin stains apical portion of tumor cells

Left: CAM 5.2+, right: synaptophysin+

Cytology description
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● Small to moderate-sized loose groups with numerous single cells, prominent acinar formation, little anisonucleosis and prominent nucleoli
● Background cleaner than ductal carcinoma
● Significant overlap with features of pancreatic endocrine tumors ( Diagn Cytopathol 2006;34:367)

Cytology images
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FNA from metastases to liver

Positive stains
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● Note: staining is often in the apical portion of the tumor cells
● BCL10 (Virchows Arch 2009;454:133), PAS (diastase resistant) for granules, trypsin and chymotrypsin (90%+ sensitive), lipase (50% sensitive), amylase, elastase, butyrate esterase (75% sensitive, indicates lipase), keratin, 2P-1-2-1 (sensitivity and specificity 100%, J Clin Pathol 2012;65:327)
● Claudin7 (Am J Surg Pathol 2009;33:768, Arch Pathol Lab Med 2008;132:490)

Negative stains
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● Mucin, CD56, PAX8

Molecular / cytogenetics
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● Amplifications at chromosome 20q (100%) and 19p (80%) (Mod Pathol 2011;24:1229)
● Kras and p53 mutations uncommon
● Biallelic inactivation of LKB1 is associated with Peutz-Jeghers syndrome

Electron microscopy description
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● Well-developed microvilli, abundant granular (rough) ER, numerous mitochondria, zymogen like granules (300-600 nm, apical, homogenous), irregular fibrillary granules (up to 3500 nm with fibrillary internal structures, resemble zymogen granules in developing pancreas)

Electron microscopy images
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Tumor cells have many pleomorphic and rather small zymogen granules (mean 400-500 nm, range 200-1000 nm), commonly oriented towards the luminal space; they are round and lack a hole between their homogeneous dark staining contents and the granule membrane

FNA from liver metastasis

Differential diagnosis
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● Ductal adenocarcinoma: mucicarmine+, CEA+, negative for acinar markers
● IPMN: papillary variant of acinar carcinoma, compared to IPMN, has nodules with more sheetlike nature, cuboidal cells, basophilic cytoplasm, prominent nucleoli, apical granules, intraluminal crystals or pale, acidophilic secretions, and lack of mucin (Am J Surg Pathol 2007;31:363)
● Pancreatic endocrine tumor: no acinar differentiation, uniform nuclear morphology, fibrous stroma, PAS-
● Pancreatoblastoma: children, squamoid bodies
● Solid pseudopapillary tumor: young women, cystic and hemorrhagic, solid and pseudopapillary patterns, CD56+, CD10+

End of Pancreas > Tumors > Acinar cell carcinoma

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