Liver metastases of pancreatic acinar cell carcinoma with marked nuclear atypia and pleomorphism diagnosed by EUS FNA cytology: a case report with emphasis on FNA cytological findings

Abstract

Background: Acinar cell carcinoma of the pancreas is a rare neoplasm. Although this tumor has been well characterized histologically, the morphological patterns in Fine Needle Aspiration Cytology have not been well defined. Unlike ductal adenocarcinomas, endocrine tumors, and solid pseudopapillary tumors of the pancreas with their characteristic FNA cytological features, acinar cell carcinomas pose a particular diagnostic challenge by sharing many cytomorphologic features with endocrine tumors of the pancreas.

Case presentation: A 37-year-old man presented with lower chest and left upper quadrant abdominal pain. Computed tomography revealed a 7.8 x 7.3 cm irregular, partially cystic mass in the body and tail of the pancreas, and two lesions in the liver compatible with metastases. Subsequently, the patient underwent endoscopic ultrasound-guided fine needle aspiration on one of the two metastatic liver masses. FNA cytology revealed abundant, loosely cohesive clusters of malignant epithelial cells with vaguely acinar and trabecular formations. The pleomorphic nuclei had fine granular chromatin and occasionally small nucleoli. There were scant to moderate amounts of cytoplasm. Scattered, strikingly large tumor cells with giant nuclei, prominent mitoses and associated necrosis were evident. A pancreatic endocrine tumor was suspected initially, but acinar cell carcinoma of the pancreas was confirmed by immunohistochemistry, cytochemical and ultrastructural studies.

Conclusion: We describe a case of pancreatic acinar cell carcinoma with unusual cytomorphologic features mimicking an endocrine tumor of pancreas, encountered in endoscopic ultrasound-guided fine needle aspiration of a metastatic liver mass and discuss the diagnostic approach for this unusual pancreatic tumor in fine needle aspiration cytology.

Figure 1

A. Endoscopic ultrasound showing the metastatic mass in the left lobe of liver with an aspirating fine needle in it. B. Electron micrograph showing clusters of spherical shape and homogenous, medium electron dense zymogen granules in the cytoplasm (arrows).

Figure 2

A. Hypercellular aspirate with sheet of pleomorphic tumor cells (Diff-Quik, ×10) B. Vaguely acinar formation (Papanicolaou stain ×20). C. Trabecular pattern (Papanicolaou stain ×10). D. Scattered large tumor cells with giant nuclei (Papanicolaou stain ×20).

Figure 3

A. On cell block, the tumor cells arranged in thick trabeculae, poorly formed glands or acini. Necrosis is evident. (H&E stain ×4); B. Solid pattern. (H&E stain ×20); C. Acinar pattern with uniform, eccentric located nuclei with abundant eosinophilic cytoplasm. (H&E stain ×20); D. Tumor cells with pleomorphic, centrally located nuclei, small to prominent nucleoli and scant to moderate amount of cytoplasm. Brisk and abnormal mitosis are evident. (H&E stain ×40)

Figure 4

A. The tumor cells are strongly positive for alpha-antitrypsin (immunoperoxidase stain ×40) B. Tumor cells with positive cytoplasmic PAS-D stain. (Periodic Acid-Schif with diastase stain ×40)