We report a patient with a minute nonfunctioning islet cell tumor, 8mm in diameter, which demonstrated malignant features by histology. The patient was a 43-year-old Japanese woman, who had an elevated carbohydrate antigen (CA) 19-9 level, of 59U/ml (normal range, <37U/ml) identified on a health check to rule out malignancies. Ultrasonography and computed tomography demonstrated a well-defined pancreatic tumor, 8mm in diameter, in the body of the pancreas. Serum levels of pancreatic hormones were within normal limits, and thus a tentative diagnosis was nonfunctioning islet cell tumor. The size of the tumor remained unchanged for 1 1/2 years, but, at this time, the serum level of CA19-9 was elevated to 253U/ml. Segmental pancreatectomy was performed because malignancy could not be ruled out. The resected specimen showed an endocrine tumor invading both the pancreatic parenchyma and the perineural spaces outside the tumor. In general, minute nonfunctioning islet cell tumors have been considered to be completely benign, but the present tumor showed clear malignant features. We might have to take surgical resection into consideration even if the size of such an endocrine tumor is minute.
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