Clinical utility of endoscopic ultrasound-guided fine-needle aspiration in mixed adenoneuroendocrine carcinoma with signet-ring cells of the pancreas: a case report and review of the literature.

A man in his 60s visited our hospital because of a pancreatic head tumor. Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) revealed that the tumor consisted of a neuroendocrine carcinoma (NEC) and adenocarcinoma, including signet-ring cell carcinoma, and that the ratio of these components was approximately 50:50. Therefore, he was diagnosed with mixed adenoneuroendocrine carcinoma (MANEC). Because of liver and lymph node metastases, systemic chemotherapy was initiated using a regimen for the NEC component based on an increase in neuron-specific enolase (NSE). Although the patient achieved stable disease after two chemotherapy cycles, the tumor increased in size after three cycles, which was associated with a gradual increase in carcinoembryonic antigen and a decrease in NSE level. An EUS-FNA reexamination revealed that the adenocarcinoma component accounted for 90 % of the tumor. Thus, an adenocarcinoma chemotherapy regimen was started, and a slight reduction in tumor size was observed. Here, we report an extremely rare and remarkable case of MANEC of the pancreas that demonstrates the effectiveness of EUS-FNA for helping to decide the chemotherapy regimen.