Histopathological study on mechanism and background of tumor-forming pancreatitis.

Fifteen cases of tumor-forming pancreatitis, detected as tumors by diagnostic imaging or by physical examination were histologically examined. Eleven of the 15 patients were heavy drinkers. Tumorous lesions were located in the head of the pancreas in 11 cases and in the body or tail of the pancreas in four cases. Macroscopic examination revealed tumorous swelling or sclerotic appearance in the pancreatic tissue. Histologically, these lesions showed tumorous swelling with (n = 12) or without (n = 3) a background of chronic pancreatitis. In the former, the tumorous lesions consisted of extensive fibrosis, including necrosis or abscesses, stones and reparative granulation tissue, and there was a successive transition to the surrounding chronic pancreatitis pattern. The latter three tumorous lesions presented with inter- and intralobular fibrosis with lymphoid hyperplasia or lymphoplasmacytic infiltration and were adjacent to normal pancreatic tissue. Therefore, tumor-forming pancreatitis shows at least two distinct types: a reparative tumorous swelling with a background of chronic pancreatitis, which is considered to have given rise to the tumor at some stage; and a lymphoid and fibrous proliferation in normal pancreatic tissue, which is considered to represent an autoimmune-related disease process.