Non-tumor forming and diffusely spreading invasive pancreatic cancer.

A 78-year-old man presented to our hospital with loss of appetite and epigastric discomfort. Computed tomography (CT) revealed dilation of the main pancreatic duct and three cystic lesions in the pancreatic neck, body, and tail. Endoscopic ultrasonography showed a mural nodule > 5 mm enhanced with Sonazoid in a cyst. Therefore, the patient was diagnosed with intra-ductal papillary mucinous neoplasm (IPMN) and underwent distal pancreatectomy. Macroscopic examination of the cut surface of the resected specimen showed no solid tumors in the pancreatic parenchyma. The histopathological diagnosis of the cysts was IPMN with low-grade dysplasia. Ten months after surgery, the serum carbohydrate antigen 19-9 level was elevated, and CT showed multiple peritoneal and pulmonary nodules, suggesting peritoneal dissemination and lung metastases. Since recurrence of pancreatic cancer was suspected, repeat histopathological examination of the resected specimen was performed, revealing small clusters of atypical epithelial cells diffusely spreading in the pancreatic tissue. The diagnosis was changed to invasive ductal carcinoma (pT2N1bM0, stage IIB). Invasive pancreatic cancer that does not form a solid mass, and shows diffuse spreading with small clusters is extremely rare. Imaging diagnosis and histopathological examination should be carefully performed in such cases.