An in situ carcinoma of the pancreas forming 2 invasive ductal carcinomas.

A 62-year-old man underwent distal pancreatectomy for invasive pancreatic carcinoma. Histopathologically, the main lesion that obstructed the main pancreatic duct and measured 2.0 cm in diameter was a moderately differentiated adenocarcinoma with marked neural invasion. The main pancreatic duct immediately distal to the tumor was lined with carcinoma in situ, and gradual transition from carcinoma in situ to mild atypia was observed. An accessory tumor measuring 0.8 cm in diameter was located in the pancreatic tail. The adjacent pancreatic contained carcinoma in situ and flat dysplastic cells without papillary growth. We concluded that the structure of the cells lining the ducts and the comparatively flat formation and gradual transition indicated that 2 lesions, each invading the pancreatic parenchyma, arose from the intraductal tumor (carcinoma in situ or precancerous lesion).