We report two cases of invasive pancreatic cancer smaller than 30 mm in diameter which were suggested to be derived from small intraductal papillary mucinous neoplasm (IPMN). The patient in case 1 was a 67-year-old man, and a 17 mm branched IPMN was detected close to a pancreatic cancer. Pancreaticoduodenectomy was performed and the two tumors were histologically revealed to be adjacent to each other. Transitional features were also detected at the boundary. The patient in case 2 was a 59-year-old man, who had been followed for a 25 mm branched IPMN at the uncus of the pancreas for two years. The solitary pancreatic cancer close to this IPMN had been newly detected and pancreaticoduodenectomy was performed. Histologically, the cystic lesion contained components of IPMN and invasive adenocarcinoma. International consensus guidelines for the management of IPMN shows the indications for resection of branched duct IPMNs as those fitting the following 5 conditions, namely, larger than 30 mm in size, the presence of a mural nodule, cytologically positive pancreatic juice, dilatated main pancreatic duct, or symptomatic. However, similar to both of these two cases, invasive pancreatic cancer can be derived from small branched duct IPMN without any mural nodule. Careful attention is thus required to follow IPMNs.
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