Immature squamous metaplasia (focal atypical epithelial hyperplasia) of the pancreatic duct—immunohistochemical distinction from intraductal carcinoma

Aims Immature squamous metaplasia of the pancreatic duct ( ISMPD ) can be difficult to differentiate from an intraductal carcinoma of the pancreas ( ICP ), and little is known about the pathological nature of ISMPD . The aim of this study was to analyse 20 ISMPD and 10 ICP tissue samples. Methods and results ISMPD shares some characteristics with ICP . Seven of 20 ISMPD samples were covered by a layer of pancreatic duct epithelium, whereas this was not seen in the ICP samples. Immunohistochemistry of ISMPD revealed positivity for p63 (100%), cytokeratin 5/6 (95%), cytokeratin 7 (95%), cytokeratin 20 (10%), and MUC ‐1 (95%), and the samples were negative for p53, carcinoembryonic antigen ( CEA ), and bcl‐2. In contrast, ICP was positive for p63 (40%), p53 (10%), cytokeratin 7 (90%), cytokeratin 20 (20%), CEA (30%), and MUC ‐1 (80%), and negative for cytokeratin 5/6. However, in 84% (16) of the ISMPD samples, cytokeratin 7 was expressed only by an epithelial layer at the apical surface; this expression pattern was not found in any of the 10 ICP samples. The mean K i67 labelling index was 1.0% in ISMPD and 18.5% in ICP . Conclusions Our study suggests that immunohistochemical staining for cytokeratin 5/6 and K i67 constitutes the best combination for differentiating ISMPD from ICP .