A rare case of pancreatic acinar cell carcinoma presenting a submucosal tumor.

A 66-year-old man, who underwent distal gastrectomy with Billroth I reconstruction for gastric cancer, regularly underwent upper endoscopy as a routine examination. Unlike 1 year earlier [Figure 1a], a submucosal tumor-like lesion was identified near the minor papilla [Figure 1b], but the opening of the minor papilla could not be confirmed. Computed tomography revealed a mass (26 mm × 10 mm) protruding from the duodenal wall into the duodenal lumen [Figure 2] without pancreatic duct dilation. EUS using a linear array echoendoscope showed that the hypoechoic and smooth-marginal mass adjacent to the pancreatic head [Figure 3a] and the accessory pancreatic duct could not be recognized. EUS using a miniature probe showed that the mass was mainly located in the muscularis propria of the duodenal wall [Figure 3b]. The initial diagnosis was a duodenal gastrointestinal stromal tumor; however, EUS-guided fine-needle biopsy of the mass revealed suspicious pancreatic acinar cell carcinoma (PACC). A pancreaticoduodenectomy was performed. Macroscopically, a gray-white mass with a 25-mm maximum diameter was found in the duodenal submucosa on the cut surface [Figure 4a]. The boundary between the mass and the pancreatic parenchyma was unclear. Predominant growth of the tumor was observed within the accessory pancreatic duct by loupe image [Figure 4b]. No invasive growth or cystic formation was found. The tumor cells having irregular, hyperchromatic nuclei and eosinophilic cytoplasm proliferated mainly in an acinar or tubular pattern [Figure 4c]. The neoplastic cells were diffusely positive for anti-trypsin [Figure 4d] and bcl-10, whereas they were negative for a neuroendocrine marker, chromogranin or synaptophysin. Finally, the pathological diagnosis was a PACC at stage TisN0M0.Figure 1: (a) Endoscopic image showing no abnormality of the duodenal wall and minor papilla 1 year ago. (b) Endoscopic image showing a submucosal tumor-like lesion near the original minor papillaFigure 2: Contrast-enhanced computed tomography showing a mass (arrow) protruding from the duodenal wall into the duodenal lumen located in contact with the pancreatic headFigure 3: (a) EUS using a linear array echoendoscope showing a hypoechoic and smooth-marginated mass outside the pancreatic head. (b) EUS using a miniature probe showing the mass mainly located in the muscularis propria of the duodenal wallFigure 4: (a) Gross examination of resected specimen revealed a gray-white, solid lesion mainly occupying the duodenal submucosa on the cut surface. (b) A tumor with intraductal growth was observed by loupe image of histologic specimen (H and E). Normal pancreatic parenchyma (arrow). (c) Tumor cells having irregular, hyperchromatic nuclei and eosinophilic cytoplasm proliferated resembling acini of the pancreas (H and E, × 200). (d) Immunohistochemically, the neoplastic cells were positive for anti-trypsin (×40)PACC is a rare pancreatic tumor,[1] which is typically a solid tumor with expansive growth.[2] A PACC that predominantly grows within the main pancreatic ducts is extremely rare.[3] There has not been any reported case of PACC growing in the accessory pancreatic duct and presenting a submucosal tumor. In this case, there are some hypotheses regarding the specific tumor appearance: PACC originating from (1) pancreatic parenchyma near the accessory pancreatic duct and (2) ectopic pancreas[4] or submucosal pancreatic parenchyma.[5] However, it is a limitation that it was difficult to prove the hypotheses. Authors’ contributions R.S. treated the patient and wrote the manuscript; H.K., H.N., S.H., T.M., K.S., T.Y., H.A., M.K., M.F., T.M., M.F., K.O., E.T., T.U., A.T., and A.I. treated the patient and contributed writing the manuscript; T.T. performed pathological diagnosis and contributed writing the manuscript; all authors approved the final manuscript. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest Masaki Kuwatani is an Editorial Board Member of the journal. This article was subject to the journal’s standard procedures, with peer review handled independently of the editor and his research group.