Gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS)
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A patient presents with numerous fundic gland polyps in the proximal stomach. Family history reveals gastric cancer in multiple relatives. No colonic polyps are found.
AD; APC promoter 1B variants (specific region)
- Distinct from classic FAP: restricted gastric phenotype
- Fundic gland polyposis (proximal stomach, >100 polyps)
- Gastric adenocarcinoma risk (intestinal type)
- No duodenal or colorectal polyposis (unlike FAP)
- Dysplasia in fundic gland polyps
- APC point variants in promoter 1B region
- Clinical criteria: fundic gland polyposis restricted to the proximal stomach (with sparing of antrum and duodenum), typically >100 polyps in the proband, with autosomal dominant inheritance and no colorectal or duodenal polyposis
- Histology shows fundic gland polyps, often with dysplasia and proximal gastric adenocarcinoma
- Confirm with germline testing identifying an APC promoter 1B point variant (YY1 binding motif); standard APC coding-region analysis is negative
- Upper GI surveillance with extensive biopsies
- Consider prophylactic gastrectomy for high-grade dysplasia or cancer
- Colonoscopy (usually normal)
GAPPS vs FAP, same gene (APC), different location: GAPPS is caused by a variant in the APC promoter 1B (a transcription factor binding site, YY1), whereas FAP is caused by loss-of-function variants in APC. GAPPS = stomach polyps and cancer only, no colon polyps (the opposite of FAP).