Gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS) is an autosomal dominant syndrome caused by germline pathogenic variants in promoter 1B of the APCgene.[
GAPPS and FAP are both caused by pathogenic or likely pathogenic variants in the APC gene, but they are distinct syndromes with different clinical characteristics. In GAPPS, polyposis and cancer risk are primarily confined to the stomach, while in FAP, polyposis and cancer risk are elevated in the colon. FAP is a hereditary cancer syndrome characterized by colorectal polyposis and a 93% risk of colorectal adenocarcinoma. Pathogenic or likely pathogenic variants in promoter 1B of the APC gene are pathognomonic of GAPPS and do not lead to FAP. In contrast, FAP is caused by germline pathogenic variants elsewhere in the APC gene or large deletions in promoter 1B. For more information about FAP, refer to the
Environmental risk factors have not been reported to cause or modify the penetrance of GAPPS. Although studies have speculated that there is an inverse relationship between gastric neoplasia and Helicobacter pylori infection, further research is warranted to clarify how H. pylori impacts gastric neoplasia in individuals with GAPPS.[
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Gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS) is caused by germline pathogenic variants in promoter 1B (regulatory region) of the APCtumor suppressor gene.[
The APCgene is located on chromosome 5q21 and encodes a 2,843–amino acid protein that is important for cell adhesion and signal transduction processes.[
A 2016 study identified that germline pathogenic variants in promoter 1B of the APC gene cause GAPPS.[
Since GAPPS was first described in the literature, over 20 families with the syndrome have been identified in Australia, North America, Europe, and Japan.[
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Consensus genetic testing guidelines specific to gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS) do not yet exist. Proposed diagnostic criteria for GAPPS include a heterozygous germline APCpathogenic variant in promoter 1B and all of the following:[
However, GAPPS should be suspected in patients with 100 or more proximal gastric polyps with antral sparing, the absence of colorectal polyposis, and the presence of a germline pathogenic variant in the promoter 1B region of the APCgene. Individuals are at the greatest risk for GAPPS if they have a biological relative with clinical features of GAPPS and/or a known germline pathogenic variant in promoter 1B of the APC gene. Clinical-grade, diagnostic genetic testing for GAPPS is available at Clinical Laboratory Improvement Amendments (CLIA)-certified laboratories. Although many laboratories in the United States offer germline APC genetic testing, only a few perform sequence analysis of promoter 1B for the pathogenic variants that cause GAPPS.[
Primary differential diagnoses for GAPPS include the following:
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Gastric Manifestations in GAPPS
A key feature of gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS) is extensive fundic gland polyposis in the proximal regions of the stomach with antral (distal) sparing. For more information, see the
Colorectal Manifestations in GAPPS
Individuals with GAPPS may also have a propensity to develop colon polyps, although polyps are not thought to develop at an earlier age than those seen in the general population.[
Clinicopathologic evaluation of two families with GAPPS phenotypes (based on clinical criteria) demonstrated that seven of nine affected individuals had colon pathology.[
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Consensus guidelines for management of gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS) do not exist, given the rarity of this syndrome and the dearth of GAPPS literature (aside from case reports or case series). Furthermore, the incomplete penetrance of GAPPS and its large age range of polyposis onset/gastric adenocarcinoma incidence makes creating uniform management recommendations challenging. The literature frequently recommends that providers use an individualized management approach for patients with GAPPS, with frequent upper endoscopic surveillance and extensive sampling of gastric polyps.[
The goal of gastric endoscopic surveillance is to detect morphological or histological changes that increase risk for gastric adenocarcinoma. Generally, the detection of fundic gland dysplasia in GAPPS prompts heightened gastric cancer surveillance with more frequent endoscopic screening and discussions about risk-reducing gastrectomy with a multidisciplinary team. However, the natural progression in histology from fundic gland polyp to adenocarcinoma (including the precursor lesion to adenocarcinoma) is unknown. It has been hypothesized that hyperproliferative crypts found on pathology may be precursors to fundic gland polyps and adenomas in patients with GAPPS.[
Given the variable penetrance of GAPPS, the correlation between gastric adenocarcinoma and clinical features (such as age, family history, degree of polyposis, and pathology of polyps) is unknown. However, given the high incidence of gastric adenocarcinoma seen in those with GAPPS (even when patients participate in gastric surveillance), discussion about risk-reducing gastrectomy with a multidisciplinary team may be warranted. Risk-reducing gastrectomy has been recommended when dysplasia is present.[
There are no consensus guidelines for colorectal surveillance in patients with GAPPS. Therefore, patients are managed based on their family histories of colorectal polyps/cancer with consideration of a baseline colonoscopy to exclude colonic polyposis.[
Level of evidence: 5
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Last Revised: 2025-01-03
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