S-1 treatment leading to complete remission of advanced duodenal adenocarcinoma: A case report.

Primary duodenal adenocarcinoma (DA) is a rare malignant neoplasm, accounting for 1% of all gastrointestinal tract carcinomas. This is the case report of a 40-year-old male patient with a duodenal lesion detected on abdominal magnetic resonance imaging and diagnosed by endoscopy and biopsy as DA. Following surgical resection and histopathological examination, the tumor was confirmed as differentiated duodenal neuroendocrine carcinoma with liver metastasis (TxNxM1). The patient received 8 cycles of palliative chemotherapy with oxaliplatin and S-1 and achieved a clinically complete response, with a treatment-related toxicity profile that was considered as tolerable. Therefore, this regimen exhibited favorable efficacy and a tolerable toxicity profile for the treatment of DA in this case.