The negative test that wasn't really an answer
For families with multiple cases of hereditary diffuse stomach cancer, the standard genetic test asks one question: do you carry a damaging change in the CDH1 or CTNNA1 gene?
When the answer is yes, families can take life-saving steps — close monitoring or even preventive removal of the stomach.
When the answer is no, families have historically been told there's nothing more to find. They're left without a clear cause and without access to the same prevention measures.
A new study suggests the answer was there all along — just in places no one was looking.
Hereditary diffuse gastric cancer is a serious inherited condition. Affected families face a sharply elevated lifetime risk of stomach cancer, often diagnosed at younger ages and with worse outcomes than typical stomach cancers.
The current standard of care for confirmed CDH1 carriers includes intensive screening or, in many cases, prophylactic gastrectomy — preventive removal of the stomach. It's a drastic step, but it can be life-saving.
But more than half of families that meet the clinical criteria for hereditary diffuse stomach cancer test negative on the standard genetic panels. Those families can't access the same prevention pathway, even though their cancer risk may be just as high.
The old way versus the new way
Standard genetic testing focuses on the parts of the genome that code directly for proteins. If the CDH1 protein-coding sequence looks normal, the test is reported as negative.
But that's only part of the genome. Surrounding the protein-coding regions are vast stretches of DNA that don't encode proteins themselves but tell those genes when, where, and how strongly to turn on. Damage to these regulatory regions can silence a gene just as effectively as a mutation in the gene itself.
The new study expanded the search to include those regulatory regions, plus larger structural changes that standard tests can miss.
How regulatory DNA controls gene activity
Imagine a stove. Standard genetic testing checks whether the burners themselves are working. But the stove also has dials that control how high each burner goes. If a dial is broken, the burner doesn't heat properly — even though the burner itself is fine.
CDH1 is the burner. Regulatory regions around it are the dials. The new analysis looked at the dials.
Some of those dials sit close to CDH1. Others sit much farther away in the genome but still control CDH1 through the way DNA folds in three dimensions inside the cell.
The study snapshot
The team analyzed whole-genome sequencing data from 19 families who met clinical criteria for hereditary diffuse stomach cancer but tested negative on standard panels. They also mapped the chromatin landscape and CDH1 promoter interactions in normal stomach tissue. Each candidate change was tested for its functional impact in cell lines using gene-editing tools and confirmed in patient tumor samples.
In nearly half of these previously unexplained families — 47% — the team identified a likely genetic cause.
In one family, a deletion that cut out a regulatory region near CDH1 reduced the gene's protein output significantly. In another family, a small deletion downstream of CDH1 had the same effect through a different regulatory mechanism. A third family carried a deletion in a separate gene called MLH1 that overlapped a stomach-specific control region for CDH1, causing tumor cells to lose both proteins.
Beyond these cases, the team also found multiple smaller deletions in regulatory regions across other genes, particularly affecting mucin proteins and immune-related pathways. These oligogenic patterns — many small contributors instead of one big mutation — appeared most often in families where cancer struck especially young.
This research uncovers causes, not yet a new test that's available everywhere.
Where this fits in the bigger picture
Genetics has been gradually moving beyond protein-coding regions for years. Studies in many cancer syndromes are showing that regulatory mutations and structural changes can cause inherited disease just as powerfully as classic gene mutations.
This work brings that broader strategy to hereditary stomach cancer, where the practical stakes are unusually high. Families currently denied access to prevention pathways could, with the right testing, be reclassified as carriers and offered the same monitoring and surgical options as confirmed CDH1 families.
If you have a strong family history of diffuse stomach cancer and previously tested negative on a standard genetic panel, this study is reason to revisit the question with a specialized hereditary cancer clinic.
Whole-genome sequencing combined with regulatory analysis isn't yet a routine clinical test for most families. But it's available through some research programs and major cancer centers. A genetic counselor familiar with hereditary stomach cancer can help you understand whether reanalysis makes sense for your family.
The study analyzed 19 families — significant for this rare condition but small in absolute terms. The functional confirmations were done in cell lines and animal models, which may not capture all the complexity of how cancer develops in living patients. Whole-genome interpretation also requires specialized expertise that isn't yet widely available in routine clinical settings.
The next steps are larger studies in similar families and the development of clinical tests that can detect these regulatory and structural changes routinely. As that infrastructure builds, more hereditary stomach cancer families should gain access to definitive answers — and to the prevention measures that come with them.