LAUSR

BACKGROUND The aim of this study was to assess the relevance of highlighting T1a invasive intraductal papillary mucinous carcinoma as a separate subcategory and to compare the tumor biology between invasive intraductal papillary mucinous carcinoma and pancreatic ductal adenocarcinoma. METHODS A total of 144 and 328 consecutive patients with intraductal papillary mucinous neoplasms and pancreatic ductal adenocarcinoma, respectively, were analyzed. RESULTS Patients with T1a invasive intraductal papillary mucinous carcinoma comprised 25% (11/44) of the overall subject population with invasive intraductal papillary mucinous carcinoma with 5-year disease-specific survival rate being 100%. None of the patients with pancreatic ductal adenocarcinoma were classified as having T1a disease. When patients with invasive intraductal papillary mucinous carcinoma and pancreatic ductal adenocarcinoma were compared after excluding patients with T1a invasive intraductal papillary mucinous carcinoma, the 5-year disease-specific survival rates were 63% vs 40% in node-negative status (P = .018); and they were 20% vs 13% in node-positive status (P = .385). Subsequent analyses revealed that this survival superiority was limited to patients without evidence of lymphatic invasion. CONCLUSION T1a invasive intraductal papillary mucinous carcinoma is a clinical entity specifically observed in patients with intraductal papillary mucinous carcinoma, but not in patients with pancreatic ductal adenocarcinoma, and is associated with excellent postoperative survival outcomes. In the survival comparison after exclusion of patients with T1a tumors, when the analysis was limited to patients without lymphatic invasion or lymph node metastasis, the disease-specific survival rate remained higher in patients with invasive intraductal papillary mucinous carcinoma compared with those with pancreatic ductal adenocarcinoma, and this difference was considered as being attributable to the intrinsic indolent biological behavior of invasive intraductal papillary mucinous carcinoma. However, this survival advantage was lost once lymphatic invasion occurred.