[1425] Mesothelin and B72.3: Can Their Expression Patterns Help Distinguish Neoplastic Cysts of the Pancreas?

S Li, D Jhala, N Jhala. University of Alabama at Birmingham, Birmingham, AL

Background: Mesothelin is a GPI-anchored cell surface protein. Previously, it has been established that it is expressed in pancreatic adenocarcinoma but not in reactive ductal epithelial cells. B72.3 is an oncofetal antigen and a known tumor associated glycoprotein which is expressed in the majority of human adenocarcinomas including colorectal, pancreatic, gastric, ovarian, endometrial, mammary, and non-small cell lung cancer. Previous studies demonstrated that it is immunoreactive in pancreatic adenocarcinoma but negative in normal pancreatic ductal cells. Little is known about mesothelin and B72.3 expression in cystic pancreatic neoplasm. Present study was undertaken to determine if mesothelin and B72.3 are differentially expressed in various cystic neoplasms of the pancreas.
Design: The study group included 52 surgically resected cases incorporating pancreatic adenocarcinoma (ACA, n= 35), intraductal papillary mucinous neoplasm (IPMN, n = 9), mucinous cyst adenoma (MCA, n= 5), and serous cyst adenoma (SCA, n = 3). Adjacent non neoplastic ducts served as control groups. Pancreatic endocrine neoplasms, pseudo cysts and solid pseudo papillary neoplasms being non epithelial tumors were not included in the study population. Percent positivity and intensity of mesothelin and B72.3 expression were determined by immunohistochemistry method using formalin-fixed, paraffin-embedded full tissue sections. A Fisher's exact test was performed to determine the difference in expression patterns.
Results: Mesothelin expression was noted in 32 of 35 cases of ACA (91%), 6 of 9 cases of IPMN (67%), 1 of 5 cases of MCA (20%), and 0 of 3 cases of SCA (0%). Mesothelin expression was diffuse and more intense in ACA, weak in IPMN, and rare weak positive expression in MCA. All 2 cases of cystic ACA were strongly positive for mesothelin. The difference was statistically significant (p = 0.0023). Benign pancreatic tissue was present in 16 cases of ACA which were all negative for mesothelin. B72.3 expression was diffuse and intense in all cases of ACA (including 2 cases with cysts) and IPMN. In contrast, it was focal and weak in MCA and SCA. B72.3 expression was statistically significantly (P = 0.03) different between IPMN and other non malignant epithelial cysts (MCA and SCA).
Conclusions: Our results suggest that both mesothelin and B72.3 may serve as powerful markers to distinguish neoplastic epithelial cysts in equivocal cases. This result can have major impact in distinguishing various neoplastic epithelial cysts on cytology specimens.
Category: Liver & Pancreas

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 227, Wednesday Morning