RESUMO
Ampullary adenocarcinoma is a rare malignancy that originates in the ampulla of Vater. It typically presents in the seventh decade of life. This condition shares overlapping features with periampullary tumors such as pancreatic cancer, but treatment modalities and prognosis vary. Histology will demonstrate either intestinal or pancreato-biliary epithelial subtype in ampullary adenocarcinoma. Despite its rare occurrence, ampullary adenocarcinoma should be included as a differential in elderly patients presenting with biliary obstruction. This case presentation is unique as it highlights the importance of histopathological findings and their progression. In this case, initial histology results revealed tubulovillous adenomatous polyps, but later biopsies revealed adenocarcinoma cells. These findings suggest that ampullary adenocarcinoma and several gastrointestinal cancers share a similar mechanism of action as it is related to the adenoma-to-carcinoma sequence. This case presentation aims to highlight the rare occurrence of this phenomenon at the ampulla of Vater.