A Subset of Pancreatoblastomas May Arise From an Adenomatous Precursor: An Ampullary Pancreatoblastoma and Adjacent Adenoma With a Shared Molecular Phenotype in an Adult Patient.

Pancreatoblastomas are rare pediatric tumors. In adults, they are exceedingly rare and seem to have a worse prognosis. Most are sporadic, though rare, cases occur in patients with familial adenomatous polyposis. Unlike pancreatic ductal adenocarcinomas, pancreatoblastomas are not believed to arise from dysplastic precursor lesions. Clinical history, along with endoscopic, pathological, and molecular findings, was reviewed for a 57-year-old male patient with an ampullary mass who presented with obstructive jaundice. Microscopic examination showed a pancreatoblastoma subjacent to an adenomatous polyp with intestinal differentiation and low-grade dysplasia. Both tumors had abnormal p53 (complete loss) and nuclear β-catenin immunostaining. Mutational panel analysis showed an identical CTNNB1 (p.S45P) mutation in both. This case adds to our understanding of the pathogenesis of these rare tumors and suggests that a subset may arise from an adenomatous precursor. In addition, this case is just the second pancreatoblastoma to originate in the duodenal ampulla, and the preceding case suggests that an ampullary location leads to earlier diagnosis. Moreover, this case highlights the difficulty in diagnosing pancreatoblastoma on limited tissue specimens and illustrates the need to include pancreatoblastoma in the differential diagnosis in all tumors in and around the pancreas, including those in adult patients.