Case Diagnosis and Discussion

Diagnosis

Acinar cell carcinoma

Discussion

Acinar cell carcinoma (ACC) is a rare, highly aggressive malignant exocrine carcinoma with acinar differentiation. It contributes to 1-2% of all primary pancreatic neoplasms and most commonly arises during the 5th-7th decades of life. The tumor is highly aggressive with a high rate of recurrence. A minority of patients will have an associated lipase hypersecretion paraneoplastic syndrome.

Grossly, the acinar cell carcinomas are solid, well-circumscribed, fleshy mass with an average size of 10 cm in diameter (range: 2-30 cm) (1). Microscopically, acinar cell carcinomas are densely cellular with multiple architectural patterns, although most commonly acinar or solid in their arrangement. The neoplastic cells typically have uniform nuclei with a central prominent nucleolus and minimal to moderate finely granular, eosinophilic to amphophilic cytoplasm (2).

Helpful ancillary studies include pancreatic exocrine enzymes staining including trypsin (97% positive), chymotrypsin (66-95%), and lipase (70-84%) (3). Immunohistochemical staining for cytokeratin 8 and 18 also usually positive. Focal staining for synaptophysin or chromogranin may be positive as well (35-54%), which may cause confusion with neuroendocrine neoplasms. PAS staining will be positive, with resistance to diastase digestion.

Common genetic alterations in acinar cell carcinomas include APC/catenin pathway (24% of acinar cell carcinoma) and allelic loss of chromosome arm 11p (50% of ACC).

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References

1. Stelow EB et al: Pancreatic acinar cell carcinomas with prominent ductal differentiation: Mixed acinar ductal carcinoma and mixed acinar endocrine ductal carcinoma. Am J Surg Pathol. 34(4):510-8, 2010

2. Matos JM et al: Pancreatic acinar cell carcinoma: a multi-institutional study. J Gastrointest Surg. 13(8):1495-502, 2009

3. Seth AK et al: Acinar cell carcinoma of the pancreas: an institutional series of resected patients and review of the current literature. J Gastrointest Surg. 12(6):1061-7, 2008