Intraductal papillary mucinous neoplasms of the pancreas are subclassified based on morphological features, and different immunohistochemical profiles have been identified in association with the subtypes. We previously reported that S100P was an early developmental marker of pancreatic carcinogenesis and that there was higher S100P expression in intraductal papillary mucinous neoplasms than in normal pancreatic ductal epithelium. However, there have been no reports on novel diagnostic markers to distinguish intraductal papillary mucinous neoplasm from nonneoplastic lesions. Surgical specimens of intraductal papillary mucinous neoplasm obtained from 105 patients were investigated using immunohistochemistry. S100P expression was not detected in normal pancreatic ductal epithelium but was detected in all intraductal papillary mucinous neoplasm cells (100%) with diffuse nuclear or nuclear/cytoplasmic staining. MUC5AC was also expressed in most of the intraductal papillary mucinous neoplasms (102/105; 97%). Furthermore, S100P was clearly expressed in the invasive component of intraductal papillary mucinous neoplasms (32/32; 100%), including perineural and lymphatic and minimal invasion. On the other hand, MUC5AC was expressed in only 23 cases of 32 invasive components (P < .01). These data suggest that the S100P antibody may be a useful marker for detecting all types of intraductal papillary mucinous neoplasms.
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