Pancreatic-type mixed acinar-endocrine carcinoma with alpha-fetoprotein production arising from the stomach: a report of an extremely rare case.

An extremely rare case of mixed acinar-endocrine carcinoma (MAEC) arising from the stomach in a 56-year-old Japanese woman is herein presented. An endoscopic examination and computed tomography showed a protruding gastric tumor and a large extragastric mass, respectively. Macroscopic observation on the surgical specimen revealed the extragastric cystic mass was continued to the intragastric tumor. Histologically, the intragastric tumor consisted of large or small solid nests with acinar appearance. The cancer cells had an ovoid nuclei and polygonal cytoplasm, which was frequently amphophilic. Immunohistochemical examination showed that the cancer cells were positive for chromogranin-A, synaptophysin, alpha-amylase, lipase, and alpha-fetoprotein (AFP) but were negative for CD56, insulin, and other hormones. Ultrastructurally, the cancer cells contained 500-nm electron-lucent zymogen granules and 230-nm electron-dense neuroendocrine granules. This tumor was finally diagnosed to be MAEC with AFP production of the stomach. Although no ectopic pancreas was found in the stomach, this tumor may originate from ectopic pancreas. As another theory, it is possible for this tumor to originate from the pluripotent stem cells in the stomach. A gastric MAEC with AFP production has not been reported previously.