FOG1 stained nine in ten gastro-oesophageal adenocarcinomas and few colonic ones

Design

Discovery from TCGA data and immunohistochemical validation series

Population

187 gastro-oesophageal and squamous carcinomas, 168 colonic adenocarcinomas and other tumour types

Primary outcome

FOG1 and CDX2 expression by tumour site

Effect

FOG1 moderate-high in 91.1% of gastro-oesophageal adenocarcinomas; negative-low in 92.9% of colonic

Mining TCGA expression data across 29 tumour types, investigators in The American Journal of Surgical Pathology (10 September 2026) found friend of GATA1 (FOG1) mRNA high almost only in gastro-oesophageal adenocarcinoma. They then stained 187 gastro-oesophageal adenocarcinomas and oesophageal squamous carcinomas, 168 colonic adenocarcinomas and a range of other tumours.

Moderate to high FOG1 expression was seen in 91.1% of gastro-oesophageal adenocarcinomas, whereas 51.3% were CDX2 negative or low. Squamous carcinomas expressed neither. Among colonic adenocarcinomas, 92.9% were FOG1 negative or low. Pancreatic (15.5%) and ampullary (11.2%) adenocarcinomas sometimes stained; breast, lung and ovarian adenocarcinomas rarely did, and many other carcinomas not at all.

This is a single-group discovery and validation, and the antibody is not yet in routine use. If it holds up, it fills a real gap: the metastatic adenocarcinoma where the question is stomach or oesophagus, and CDX2 is unhelpful.

• Remember CDX2 is negative or weak in about half of gastro-oesophageal adenocarcinomas.
• Treat FOG1 as a promising marker of upper GI origin, pending independent validation.
• Expect some pancreatic and ampullary adenocarcinomas to stain; FOG1 will not separate those from gastric primaries.
• Use clinical and radiological correlation for any carcinoma of unknown primary.

Why it matters

Upper GI adenocarcinoma has lacked a sensitive and specific marker, which leaves metastatic cases unresolved.

Don't overread it

One group's series; sensitivity and specificity may fall in other laboratories with other antibody clones.

The statistics, in plain English

Sensitivity is how often the marker is positive in the tumour you are looking for (91% here); specificity is how often it is negative in tumours you are not (about 93% in colon). Both were measured by the group that discovered the marker, which tends to give optimistic figures.

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