Mixed neuroendocrine-non-neuroendocrine neoplasm with mucinous adenocarcinoma and amphicrine carcinoma components in the bile duct: an autopsy case.

We report the first case of bile duct mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN) that had a mucinous carcinoma component. An 88-year-old man with biliary obstruction was diagnosed as having distal bile duct cancer using imaging examinations and endoscopic biopsy. The patient received the best supportive care without surgical resection for 13 months until death. An autopsy revealed a bulky mass involving the distal bile duct and multiple metastases in intra-abdominal lymph nodes, the liver, and the lungs. The primary cancer was microscopically diagnosed as a MiNEN, which consisted of mucinous adenocarcinoma and large cell-type neuroendocrine carcinoma (NEC) components. Metastatic lesions in the liver and lungs were composed of only NEC with rich extracellular mucin without adenocarcinoma cells. Using electron microscopy and immunohistochemistry, it was proved that all NEC cells in both primary and metastatic lesions had amphicrine features. On the basis of pathological findings, we thought that the MiNEN was initially derived from a mucinous adenocarcinoma that dedifferentiated to amphicrine NEC cells with mucin production.