Background/Aims: It is still controversial that hyperplastic epithelial lesions of the pancreatic duct are always pre-neoplastic conditions. This is an attempt to reclassify 'hyperplastic lesions' apart from low-grade neoplastic lesions, such as intraductal papillary-mucinous adenoma or low-grade intraepithelial neoplasia. Methods: To compare the features of mucin phe-notype, genetic alteration and proliferative activity between 'hyperplastic lesions' and low-grade neoplastic lesions by reviewing previous studies by ourselves and others. Results: The MUC1 and MUC2 double-negative phenotype should be considered as the characteristic expression pattern of 'hyperplastic lesions' in terms of equality to that of the normal pancreatic duct. K-ras mutation was not always observed in neoplastic lesions. Proliferative activity, represented by Ki-67 labeling index, of 'hyperplastic lesions' was significantly different from low-grade neoplasia. Conclusions: 'Hyperplastic lesion' should be treated as a pure term representing morphological features, separated from the connotation of low-grade neoplasia.

Copyright © 2007 S. Karger AG, Basel

Hyperplastic and dysplastic epithelial lesions of the pancreatic ducts were first suggested to be histological precursory lesions of invasive ductal adenocarcinoma in 1954 [1]. Since then, these lesions have been reported using up to 70 different names, such as 'lesion', 'metaplasia', 'hyperplasia', 'dysplasia' and 'neoplasia'. Their biological natures have also been variously estimated, from secondary phenomena due to obstruction caused by the tumor itself to real pre-neoplastic conditions [2]. It might be natural that they were considered to be precancerous lesions, because they are frequently found in the pancreas with carcinoma [3, 4]. However, lesions showing the same morphological features were also frequently observed at autopsy in patients free from pancreatic diseases [5, 6].

Nowadays, proliferative epithelial lesions of the pancreatic duct with slight or no dysplasia are treated as one of the following categories: low-grade intraepithelial neoplasia, termed 'Pancreatic intraepithelial neoplasia (PanIN)-1A/B';

low-grade intraductal papillary mucinous neoplasm, known as 'intraductal papillary-mutinous neoplasm (IPMN) adenoma'; or just 'hyperplasia' in the strict sense. Considering that both PanIN and IPMN represent neoplastic lesions, the term 'hyperplasia' should be applied to lesions that do not progress into carcinoma. However, there is some doubt as to whether morphologically similar lesions should be divided into different concept of pathology. The following is a review and discussion of the studies of the above-mentioned 'hyperplastic lesions', namely low-grade PanIN and IPMN.

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