Primary adenocarcinoma of the fourth portion of the duodenum, an unsuspected diagnosis.

Small bowel adenocarcinoma is a rare tumor accounting for only 0.3-0.4% of all gastrointestinal tumors, with duodenal adenocarcinoma being the most common subtype. In most patients, it presents with nonspecific signs and symptoms, often leading to a delay in diagnosis. Therefore, it is essential to establish an adequate initial clinical suspicion to carry out an adequate diagnostic approach, being necessary to perform both radiological and endoscopic diagnostic techniques.