α-Fetoprotein-Producing Hepatoid Gastric Adenocarcinoma With Osteoclast-Like Giant Cells and Neuroendocrine Differentiation

Here we present the case of a 73-year-old woman with an ulcerated, advanced, hepatoid, and α-fetoprotein-producing poorly differentiated (G3) primary gastric adenocarcinoma pT3 N3a M1 with multinucleated cells and evident neuroendocrine component. This tumor was consistent with giant cell tumor type gastric carcinoma with osteoclast-like giant cells (OGCs). The cancer was HER2 and E-cadherin negative, chromogranin A dispersedly and moderately positive, and strongly α-fetoprotein-positive with evident CK AE1/AE3 immunoreactivity, while OGCs expressed CD68. To provide an insight into the molecular background of this peculiar neoplasm, next-generation sequencing (NGS) was performed to analyze the 50 most frequently mutated oncogenes and tumor suppressors. We detected mutations in the primary tumor in the following genes: KIT, EGFR, PTEN, ATM, and RB1. In the liver metastasis, we revealed mutations in 3 genes: PIK3CA, KIT, and CDKN2A.