OBJECTIVETo study the pathologic features, diagnosis, differential diagnosis and molecular characteristics of intraductal tubulopapillary neoplasm of the pancreas (ITPN).

METHODSThe clinical findings, morphologic features, immunophenotype (by EnVision method) and KRAS gene alterations (by reverse transcriptase-polymerase chain reaction) of 6 cases of ITPN encountered during the period from January, 2001 to June, 2010 were analyzed.

RESULTSThere were altogether 2 males and 4 females. The mean age of the patients was 64 years. Gross examination showed that the tumors were located in large pancreatic ducts and appeared as polypoid nodules with ductal obstruction. Solid tumor nodules associated with adjoining dilated ducts were identified in one case. Histologically, the tumors were characterized by tubulopapillary growth pattern without luminal mucin. The tumor cells showed high-grade nuclear atypia with scanty intracytoplasmic mucin. Intraductal necrotic foci were frequently observed. Immunohistochemical study showed that the tumor cells expressed CK7 and CK19. Focal positivity for MUC5AC was demonstrated. Two cases expressed MUC1. The staining for MUC2 was negative. KRAS gene mutations were identified in 2 cases, with a single-amino-acid substitution in codon 12 (35G > A and 35G > T/34G > A).

CONCLUSIONSITPN is a newly described pancreatic intraductal neoplasm and different from intraductal papillary mucinous neoplasm. ITPN is characterized by intraductal tubulopapillary growth pattern, severe cytologic atypia and scanty mucin secretion.