Intraductal Papillary Mucinous Neoplasms: Can Mesothelin Expression Help us to Classify them Better?

Abstract

Mesothelin is a cell surface protein and a differentiation antigen of mesothelial cells. Rcently, Mesothelin expression has been reported in mucinous neoplasms of the pancreas. The aim of this study is to study the expression of Mesothelin in Intraductal pancreatic mucinous neoplasms (IPMN) and to see if this can be used to identify lesions with increasing dysplasiaA retrospective search of our Surgical database from 2008‐2014 was done. 30 cases of mucinous cystic lesions of the pancreas were identified. Clinical data including the age, size of lesion, main or branch duct involvement and pathological features including size of lesion, presence of adenocarcinoma, histopathology of the lesion were collected. All the cases were reviewed to select a representative section with the worst lesion on histopathology. The block was recut to obtain 2 unstained slides per block. One was stained with Hematoxylin and Eosin and the other was stained for Mesothelin (Leica RTU Clone5B2). Mesothelin staining pattern was evaluated as shown: Mesothelin stain Pattern Cytoplasmic Luminal/Apical Intensity Weak, Intermediate, Strong Weak, Intermediate, Strong 73% of the mucinous cystic lesions were IPMN, with 21 female patients and 9 male patients. The mean size of the lesion was 3.1 cm. A. Histopathology Number Mesothelin positive Apical stain positive 1. IPMN 16 13 4 2. IPMN with high grade dysplasia 3 3 3 3. IPMN with adenocarcinoma 3 2 2 4. Mucinous cystadenoma 2 1 0 5. Mucinous cystic neoplasm 6 1 0 B. Relation to duct 1. Main duct 8 7 6 2. Branch duct 8 6 2 3. Mixed 3 2 0 4. Not reported 3 2 1 Mesothelin shows strong luminal expression in IPMN associated with high grade dysplasia and adenocarcinoma. It can possibly be used to identify lesions which might recur or as a marker of poor prognosis, hence helpful in stratifying patients who need close follow up. It shows cytoplasmic granular positivity in neoplastic epithelium and is negative in benign pancreatic and duodenal epithelium, which may help in identifying lesional tissue. This feature may also be useful in stratifying FNA specimen which usually have scant cells. Long‐term follow up studies can be helpful to study association with recurrence and prognosis, and identify cases which require close follow‐up.