The case of a 63-year-old male with a large mass in the pancreatic tail and multiple liver metastases, diagnosed as acinar cell carcinoma of the pancreas with a few scattered endocrine cells by liver biopsy is presented. The S-1 chemotherapy was effective, and partial response was obtained with decreased levels of serum CA19.9 and NSE. Ten months after starting chemotherapy, the tumor began to grow accompanied by marked elevation of serum NSE levels (266 ng/ml). The patient died of liver failure due to multiple liver metastasis 18 months after the initiation of the S-1 chemotherapy. Histological findings at autopsy were acinar cell carcinoma with an endocrine component of more than 30 %; the final diagnosis was mixed acinar-endocrine carcinoma of the pancreas. This pathological change and clinical course may imply that S-1 was effective against the acinar component but less effective against the neuroendocrine component caused by tumor differentiation.
Keywords: Acinar cell carcinoma; Mixed acinar-endocrine carcinoma; Pancreas; S-1.