A Case of Focal Small-cell Neuroendocrine Carcinoma in the Vicinity of the Extrahepatic Bile Duct, Adjacent to an Extensive Biliary Intraepithelial Neoplasm: A Diagnostic Challenge with Major Clinical Implications.

Gastroenteropancreatic neuroendocrine tumors are known for their aggressiveness. Diagnosis of various bile duct pathologies, like biliar intraepithelial neoplasm, mixed adenoneuroendocrine carcinomas or small cell carcinomas, is challenging. This case report focuses on a rare case of a focal primary minute small cell carcinoma in the vicinity of the extrahepatic bile duct, presenting itself next to an extensive biliar intraepithelial neoplasm. This finding led to adjuvant chemotherapy, followed by major surgery. Therapeutic approach was based on CT and MRI scans but most importantly on immunohistochemistry and histological evaluation. Initially CR seemed achievable, but metastases were to be found rapidly. The authors want to underline the fact that major clinical decisions are based on sometimes tiny specimens; as literature shows it is absolutely advisable to use markers to differentiate the dignity of investigated areas. The authors call for keeping collision of tumors in mind and adding KOC staining and using it in a routine manner examining biliary duct lesions.