An 84-year-old man, who was being followed up after lobectomy for lung carcinoma, was referred for evaluation of a dilated main pancreatic duct (MPD) from the body to the tail. Endoscopic ultrasonography demonstrated a low-echo mass occupying the MPD from the body to the tail. Endoscopic retrograde pancreatography showed an occlusion of the MPD in the body, and brush cytology indicated malignant cells. Distal pancreatectomy was performed. Grossly, a white-yellow, irregular-shaped solid mass without macroscopic mucus filled the lumen of the MPD. Histologically, the mass consisted of a complex fusion of tubular glands with atypical nuclei, which did not have intracellular mucus and oncocytic cytoplasm. The tumor mass showed abrupt transition to the normal epithelium. Immunohistochemically the tumor cells were partially positive for mucin 1 (MUC1) and MUC6, and negative for MUC2, MUC5AC, and lipase. Unfortunately the patient died of brain metastasis from lung carcinoma 15 months later. A review of reported cases of intraductal tubular tumors of the pancreas showed that the present case involved characteristics and immunohistochemical staining pattern similar to those of intraductal tubular carcinoma, although it might not be described as a typical intraductal tubular carcinoma under the existing Japanese rules.

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This report describes serial observations of the growth process of a small invasive ductal carcinoma (IDC) of the pancreas from imaging studies. Histopathological studies showed IDC with macroscopic retention cysts proximal to an intraductal papillary-mucinous adenoma with mild atypia of the branch duct type in the pancreatic body, with no relation between the two lesions. IDC was demonstrated as an extremely low-echoic mass resembling a cyst with an unclear margin on the initial endoscopic ultrasonography. We misinterpreted the lowechoic mass as a benign intraductal mucinous-papillary neoplasm (IPMN) based on findings of other imaging studies, and the patient was followed-up. The mass increased from 7 mm to 13 mm in diameter over 22 mo, and remained smaller than 10 mm in diameter for about 420 d. The tumor volume doubling time was 252 d. The Ki67 labeling index was 15.9%, similar to that described in previous reports. Hence, IDC may grow slowly while remaining small.

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