Joaquin Ponce-zepeda, Wafaa A. Elatre
Clinical summary
69-year-old male was identified to have a 7.0 cm mass involving the body of the pancreas on CT Abdomen. Gastroenterology was consulted, and an Endoscopic Ultrasound (EUS) procedure was performed.
The EUS showed a large, heterogeneous, round mass in the pancreatic body with extension into the neck of the pancreas, measuring 4.0 cm by 3.0 cm. The borders of the mass were poorly defined by ultrasound. The remainder of the pancreas appeared atrophied as it was surrounded by adipose tissue.
Fine needle aspiration was performed with a 25 gauge needle using a trans-gastric approach.
Cytology description
The cytology specimen obtained during EUS consisted of 2 smears (Diff Quick preparations), and one cell block. Overall the smears and the cell block preparation contained exemplary cellularity, displaying multiple groups, cohesive clusters, and single acinar cells. The Diff Quick smears demonstrated a monomorphic acinar cell population with hyperchromatic nuclei predominantly in clusters.
The cell block displayed clusters of acinar cells with round nuclei, and abundant finely vacuolated to granular cytoplasm. Morphologically the smears and cell block constructed a picture of an acinic cell neoplasm (Figure 1, 2), therefore immunohistochemistry was performed to help confirm the diagnosis. The following immunohistochemistry was performed: AE1/AE3, CA 19.9, BCL-10, CK7, CK20, NKX 3.1, Trypsin, Chymotrypsin, PSA, INSM-1, Chromo-A, Synaptophysin, and Ki-67.
The immunohistochemistry resulting positive included AE1/AE3, CA19.9, and BCL-10 (Figure 3). The Ki-67 was identified to have an increased proliferation rate (>70%), and the remaining immunohistochemical and special stains were negative. Therefore, the morphology and immunohistochemical profile were both confirmatory of an Acinic Cell Carcinoma.
Figure 1 (Low power magnification of cell block material)
Figure 2 (Higher magnification showing a cluster of pancreatic acinar cells with round nuclei and abundant finely granular cytoplasm.)
Figure 3 (BL10 immunohistochemistry stain, staining positive in the acinar cell population.)
Discussion
Pancreatic acinar cell carcinoma (ACC) is a rare, aggressive exocrine tumor that is relatively still a mystery in the scientific community. Recent studies have identified frequent aberrant DNA methylation, abundant chromosomal amplifications and deletions suggesting defective DNA repair. Pancreatic ductal adenocarcinoma is the most common malignancy seen in the pancreas, however it is molecularly distinct from Acinar Cell Carcinoma as Pancreatic ductal adenocarcinoma has no recurrent point mutations. Studies have shown the tumor suppressor genes ID3, ARID1A, APC and CDKN2A as potential drug targets for Acinic Cell Carcinoma of the pancreas. Currently the gold standard of treatment is surgical resection, if permitting, along with gemcitabine based chemotherapy or radiofrequency ablation. In this case, the elected approach was chemotherapy, and in April 2024, CT abdomen is measuring the mass to be 5.4 cm which significantly decreased in size compared to October 2023 imaging. Currently the patient is doing well, and the plan is for total pancreatectomy with splenectomy and vascular reconstruction 3 weeks after the last day of chemotherapy.