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Abstract

Background: Gastric Adenocarcinoma with enteroblastic differentiation (GAED) is a rare subtype of AFP-producing gastric cancers characterized by a tubulo-papillary pattern resembling fetal gastrointestinal epithelium. It expresses at least one of the following enteroblastic markers (EMs): glypican-3 (GPC3), spalt-like transcription factor 4 (SALL4), and α-fetoprotein (AFP). Case Report: A 78-year-old man with a history of chronic dry cough was found to have multiple fluorodeoxyglucose avid lung nodules with CDX-2 positivity on immunohistochemistry (IHC). Next Generation Sequencing (NGS) and Caris GPSai were inconclusive. Endoscopy revealed a fungating mass at the gastroesophageal junction. Histology revealed well-differentiated adenocarcinoma with mucinous features. IHC was positive for SALL-4 and GPC3. HER2 expression returned a 3+ score. Alpha-fetoprotein (AFP) level was elevated. The patient was started on capecitabine and oxaliplatin in addition to trastuzumab with subsequent clinical and radiological improvement. Conclusion: GPC3 expression is the most sensitive marker for GAED. High serum AFP levels directly correlate with the strength of immunostaining and are associated with a poor prognosis. High HER2 expression and PDL-1 immunostaining is commonly seen in GAED cases with the most common mutation being p53. Currently, there are no set guidelines for management of GAED. Unresectable, metastatic HER2 positive conventional adenocarcinoma is being managed using platinum-fluoropyrimidine doublet therapy with anti-HER2 monoclonal antibody trastuzumab. This case report calls for aggressive IHC staining for prompt diagnosis where necessary as well as proper guidelines for management.

DOI

10.55729/2000-9666.1548

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