Well-differentiated acinar cell carcinomas will recapitulate the acinar cell lobules of the normal pancreas, forming small lumina. However, in this moderately-differentiated example, the neoplastic cells do not form lumens, rather, they are arranged in a compact trabecular pattern. Poorly-differentiated neoplasms will form solid sheets.
Despite the lack of lumen formation, the morphology of the lesional cells provide helpful clues. Neoplastic acinar cells have basally oriented nuclei, granular cytoplasm and a single prominent nucleolus.
A different tumor shows more evidence of acinar differentation.
Acinar cell carcinoma is a malignant epithelial neoplasm of pancreas which elaborates exocrine enzymes. They account for 1-2% of pancreatic exocrine tumors. Key histologic features include rather uniform cells with granular basophilic granular cytoplasm with a large nuclei and a prominent nucleoli. They grow in sheets and cords and sometimes will form acinar structures.
IHC studies will reveal positivity for trypsin, lipase and chymotrypsin. Interestingly, many are negative for amylase. Cytokeratins (keratin 8 and 18, CAM5.2 and AE1/AE3) will also be positive.
One-third of acinar cell carcinomas will exhibit positivity for chromogranin and synaptophysin and if the endocrine component is greater than 25%, the tumor is classified as a mixed acinar-endocrine carcinoma. Tumors that demonstrate mucin production or positivity for glycoproteins (CEA or CA19.9) can be classified as mixed acinar-ductal carcinomas.1,2
Occurs mainly in adults (mean age of 62 years), although cases have been reported in children and adolescents. There is a male predilection (2:1).
Most patients present with symptoms due to the mass effect of the lesion (nausea, vomiting and abdominal pain). Up to 15% develop metastatic fat necrosis in the subcutaneous tissue, bone marrow and abdomen as a result of lipase produced by the neoplasm. These patients also exhibit peripheral eosinophilia and polyarthralgias.1
The mass is often quite large (average 10 cm); the head is the preferred location, although it can be found in the tail.
Resection +/- chemotherapy for palliation.
Dismal. 5 year survival rate is 5-6%.1
→IHC profile: positive for pancreatic enzymes (trypsin, chymotrypsin, lipase and less so amylase) and positive for keratin antibody CAM2.5 and AE1/AE3.
→Ultrastructurally, membrane-bound electron-dense granules (300 to 1000 nm) can be seen and are zymogen granules. This is consistent with their acinar cell derivation. Remember that acinar cells in the normal pancreas secrete enzymes. On H&E, these granules are PAS-positive and diastase-resistant.
1 Iacobuzio-Donahue CA, Montgomery EA. Gastrointestinal and Liver Pathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elsevier; 2005: 482-484.
2 Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 476-477.