Home Cancer Gene Mutations and Fusions MET Amplification Test: Lung Cancer, Gastric Cancer, Copy Number Gain, and Result...

MET Amplification Test: Lung Cancer, Gastric Cancer, Copy Number Gain, and Result Meaning

By
Vita Library
-
2
Understand MET amplification test results in lung and gastric cancer, including FISH ratios, NGS copy number, polysomy, high-level amplification, resistance, and treatment implications.

A MET amplification test checks whether tumor cells contain extra copies of the MET gene, which can activate growth signaling and sometimes create a therapeutic target. The result is most often discussed in non-small cell lung cancer (NSCLC), where MET amplification can be a primary driver or an acquired resistance mechanism after treatment of another driver such as EGFR. It is also found in a small, biologically aggressive subset of gastric and gastroesophageal cancers. The main interpretation challenge is that “MET copy-number gain” is not a single standardized result. FISH, next-generation sequencing (NGS), and other methods use different measurements and cutoffs, and simple chromosome 7 gain is not the same as focal high-level MET amplification. MET amplification is also distinct from MET exon 14 skipping and from c-MET protein overexpression. The most useful report therefore states the assay method, copy-number or MET/CEP7 ratio, degree of amplification, and relevant co-alterations.

  • A positive MET amplification result means the tumor has increased MET gene copies, but the clinical significance is strongest when amplification is focal and high level.
  • FISH often reports a MET-to-CEP7 ratio and/or average MET copies per cell; NGS reports copy-number estimates that are not directly interchangeable with FISH values.
  • In lung cancer, MET amplification may occur at diagnosis or emerge as resistance to EGFR-targeted therapy, especially after osimertinib.
  • MET amplification is different from MET exon 14 skipping and c-MET protein overexpression; each biomarker has different tests and treatment evidence.
  • A negative result does not exclude another MET alteration or another oncogenic driver, and borderline copy gain may require confirmatory testing.

Table of Contents

What MET Amplification Means

MET encodes a receptor tyrosine kinase that binds hepatocyte growth factor. Normal MET signaling helps regulate cell growth, movement, survival, and tissue repair. Cancer cells can activate this pathway in several ways, including gene amplification, exon 14 skipping, certain mutations or fusions, and protein overexpression.

MET amplification means the tumor has gained extra copies of the MET gene. When the gain is sufficiently high and focal, it can produce strong MET signaling that helps drive tumor growth. However, not all copy-number gain has the same biologic importance.

The MET gene lies on chromosome 7. A cancer cell can gain extra copies of the entire chromosome, a state sometimes called polysomy 7, and thereby acquire more MET copies without selectively amplifying MET itself. Alternatively, the tumor can develop a focal high-level amplification in which MET copies increase disproportionately compared with the rest of chromosome 7. The latter pattern is more likely to represent true oncogenic MET dependence.

This is why a report that says “MET copy number 6” cannot be interpreted reliably without knowing the method and reference. Six copies measured by one NGS assay may not correspond to the same biologic state as six signals per nucleus by FISH. Tumor purity and computational normalization also affect NGS copy-number estimates.

MET amplification is not MET exon 14 skipping

MET exon 14 skipping is a sequence/splicing alteration that removes a region needed for normal receptor degradation, causing MET protein to persist. It is an established actionable driver in NSCLC with specific approved MET inhibitors. MET amplification is a separate mechanism and has a less standardized treatment threshold.

Similarly, c-MET overexpression is usually measured by immunohistochemistry and reflects protein abundance. A tumor can overexpress MET without high-level gene amplification, and an amplified tumor can show variable protein expression depending on technical and biologic factors.

How MET Amplification Is Tested

The two most common approaches are fluorescence in situ hybridization (FISH) and next-generation sequencing (NGS).

FISH

FISH uses fluorescent probes for the MET gene and a chromosome 7 reference, commonly CEP7. A technologist counts MET and CEP7 signals in tumor nuclei. The laboratory may report:

  • average MET copies per nucleus;
  • average CEP7 copies per nucleus;
  • the MET/CEP7 ratio; and
  • a categorical result such as nonamplified, low/intermediate amplification, or high-level amplification.

A high MET/CEP7 ratio supports focal amplification because MET copies have increased more than the chromosome reference. In contrast, a tumor with many MET signals and many CEP7 signals may have chromosome 7 polysomy rather than focal MET amplification.

There is no globally uniform cutoff. Published studies and clinical trials have used different thresholds, including ratios around 1.8 to 3.0 or average gene-copy-number values from about 5 to 10 or higher. A result must therefore be interpreted using the specific laboratory’s validated criteria and the clinical trial or treatment evidence being considered.

NGS

NGS can detect copy-number changes while simultaneously identifying mutations, fusions, and other drivers. This is efficient when a small tumor sample must answer many biomarker questions. However, NGS copy number is an estimate, influenced by tumor purity, ploidy, assay design, sequencing depth, and the bioinformatic algorithm.

A low-level NGS gain may not confirm focal amplification by FISH. Studies comparing the methods show imperfect concordance, especially at modest copy-number levels. High-level events are more likely to agree.

Tissue and liquid biopsy

Tissue remains important for copy-number assessment because it allows direct evaluation of tumor cells. Plasma NGS can sometimes identify high-level MET amplification, particularly in patients with substantial circulating tumor DNA, but a negative plasma result cannot exclude tissue amplification.

When MET amplification is being evaluated as an acquired resistance mechanism after targeted therapy, a new tissue biopsy can provide additional information about histologic transformation, tumor heterogeneity, and coexisting resistance alterations that plasma alone may not show.

How to Interpret Copy-Number Results

MET amplification results are best interpreted in levels rather than as a simple positive/negative marker.

High-level focal amplification

High-level amplification is the pattern most likely to indicate that MET is acting as a dominant oncogenic driver. It can occur in a small subset of treatment-naive NSCLC and in tumors that acquire MET dependence after another targeted therapy. Clinical responses to MET-directed drugs have generally been stronger in tumors with higher amplification levels than in tumors with modest gain.

Intermediate or low-level gain

Low or intermediate copy-number gain is harder to interpret. It may reflect tumor aneuploidy, chromosome 7 gain, a subclonal event, or a biologically weaker MET signal. In these cases, the MET/CEP7 ratio, absolute copy number, coexisting drivers, tumor fraction, and assay method become especially important.

A low-level gain on a broad NGS panel should not automatically be treated as equivalent to a high-level FISH-amplified tumor. Confirmatory FISH can be useful when the treatment decision depends on distinguishing focal amplification from polysomy.

Negative result

A negative MET amplification result means no amplification was detected by the assay’s criteria. It does not rule out MET exon 14 skipping, MET protein overexpression, or other driver alterations. A complete NSCLC workup may still need sequencing or RNA-based testing for other actionable genes.

Borderline or equivocal result

Borderline FISH ratios, poor signal quality, low tumor cellularity, or heterogeneous amplification can lead to an equivocal interpretation. The laboratory may recount additional nuclei, review another tumor area, test a second block, or compare with NGS.

MET Amplification in Lung Cancer

MET amplification is clinically important in NSCLC in two major settings: as a primary alteration present before targeted therapy and as a secondary resistance mechanism that develops under treatment pressure.

Primary MET amplification

De novo MET amplification occurs in a minority of NSCLC cases. Reported frequencies vary because studies use different thresholds, but high-level focal amplification is uncommon. When present at a high level and without another dominant driver, MET may function as the main oncogenic engine.

The distinction from MET exon 14 skipping is essential. A tumor can have one, both, or neither alteration. MET exon 14 skipping has clearer established drug-selection criteria, while amplification evidence depends more strongly on amplification level and clinical context.

Acquired resistance in EGFR-mutant lung cancer

MET amplification is one of the most important bypass mechanisms of resistance in EGFR-mutant NSCLC. Under pressure from an EGFR tyrosine kinase inhibitor, a tumor can amplify MET and activate downstream pathways despite continued EGFR blockade.

This is especially relevant after progression on osimertinib. In that setting, repeat molecular testing may identify MET amplification together with the original EGFR driver. The finding can support clinical strategies that inhibit both EGFR and MET rather than simply switching to a MET inhibitor alone.

Tumor heterogeneity can complicate testing. One progressing lesion may be MET-amplified while another is not, and plasma may capture a mixture of resistant clones. A result obtained at diagnosis may therefore no longer represent the dominant biology after several lines of therapy.

MET Amplification in Gastric Cancer

MET amplification occurs in a small subset of gastric and gastroesophageal adenocarcinomas. When it is high level, it is often associated with aggressive behavior, advanced disease, and substantial intratumoral heterogeneity.

A major challenge is that MET-amplified gastric cancers can contain geographically distinct amplified and nonamplified regions. A small biopsy may therefore underrepresent the tumor. Amplification can also coexist with gains of other genes, including oncogenes on chromosome 7, which can complicate both biology and treatment response.

Unlike HER2, where standardized testing algorithms are well established in gastric cancer, MET amplification has not reached the same level of routine treatment standardization. Multiple MET-directed strategies have been studied, but results have varied, partly because patient-selection thresholds and biomarker definitions differed.

For an individual patient, the result is most useful when it is clearly high-level, confirmed by a reliable assay, and interpreted with the full molecular profile. Broad NGS may reveal other targetable alterations or markers with stronger established treatment implications.

Treatment and Resistance Implications

The practical value of MET amplification depends on how much amplification is present and why it arose.

In treatment-naive NSCLC with high-level focal amplification, selective MET inhibitors have demonstrated activity in clinical studies, and some guidelines and specialist practices recognize high-level MET amplification as a potential treatment target. However, the evidence base and regulatory status are not identical to MET exon 14 skipping.

In EGFR-mutant NSCLC with acquired MET amplification, combination strategies are especially important. Studies have evaluated selective MET inhibitors such as tepotinib, savolitinib, or capmatinib together with EGFR inhibitors such as osimertinib. The rationale is straightforward: if the cancer is using both the original EGFR driver and a new MET bypass pathway, blocking only one pathway may be insufficient.

Clinical-trial eligibility often defines MET amplification using a particular assay and threshold. A patient may therefore qualify for one study but not another despite having the same broad phrase “MET amplified” on a report. The raw biomarker criteria should be checked against the trial protocol.

In gastric cancer, MET-targeted treatment remains more context-dependent. High-level amplification can support referral for a molecularly selected trial, but the result should not be presented as a guaranteed predictor of benefit. Heterogeneity, co-amplifications, and alternative signaling pathways can limit response.

Limitations and Next Steps

The biggest limitation of MET amplification testing is lack of a single universal definition. FISH ratios, absolute copies per cell, NGS copy estimates, and protein expression answer related but different questions. A result can only be interpreted correctly when the method is known.

Common pitfalls include:

  • calling chromosome 7 polysomy “MET amplification” based only on absolute MET signal count;
  • assuming an NGS copy number uses the same cutoff as a FISH study;
  • treating low-level gain as equivalent to high-level focal amplification;
  • confusing MET amplification with MET exon 14 skipping; and
  • relying on a negative plasma result to exclude tissue amplification.

When MET amplification is reported, useful follow-up questions are:

  1. Was the test FISH, tissue NGS, or plasma NGS?
  2. What was the MET/CEP7 ratio or absolute copy-number estimate?
  3. Did the laboratory classify the result as low, intermediate, or high level?
  4. Is the finding focal, or could it reflect chromosome 7 polysomy?
  5. Is another driver present, and was the sample obtained before or after targeted therapy?
  6. Does the proposed drug or trial use the same biomarker definition?

If a low-level NGS result would change treatment, confirmatory FISH can be reasonable. If an EGFR-mutant lung cancer progresses after targeted therapy, repeat tissue and/or plasma profiling can help identify acquired MET amplification and other resistance mechanisms. For gastric cancer, sampling more than one area may be informative when heterogeneity is suspected and sufficient tissue is available.

Practical examples of why the cutoff matters

Suppose an NSCLC NGS report lists an estimated MET copy number of 5.5. That number may sound “amplified,” but it is not enough by itself to conclude that the tumor has high-level focal MET amplification. The value could be influenced by tumor purity, ploidy, and chromosome 7 gain. If access to a MET-directed trial requires a high MET/CEP7 FISH ratio, confirmatory FISH may show that the tumor is only polysomic and does not meet the study definition. The opposite can also happen when a high-level focal event is undercalled by an NGS algorithm in a low-purity specimen.

Timing provides another important clue. If a newly diagnosed lung adenocarcinoma has no EGFR, ALK, ROS1, or other dominant driver and shows very high focal MET amplification, MET may be the primary oncogenic driver. If an EGFR-mutant cancer that responded to osimertinib for two years later develops MET amplification while retaining the original EGFR mutation, the same biomarker is more likely acting as a bypass-resistance mechanism. In the second setting, combined EGFR and MET inhibition has a stronger biologic rationale than treating the new MET finding as though it replaced EGFR entirely.

A gastric cancer result also requires attention to heterogeneity. One biopsy fragment may show striking MET amplification while another area is negative. If treatment depends on MET dependence, a small positive focus may not represent the whole tumor. Pathologists may correlate in situ hybridization with protein expression and with sampling from primary and metastatic sites when available. Co-amplification of neighboring chromosome 7 oncogenes can further complicate the assumption that MET alone is driving the cancer.

For follow-up, the most useful report preserves the original quantitative data. Terms such as “low,” “intermediate,” and “high” are convenient, but future trials may use different thresholds. Knowing the original MET/CEP7 ratio, average copies per cell, or NGS copy estimate lets the oncology team compare the result with a specific protocol rather than relying on a vague historical label.

Because MET criteria continue to evolve, a borderline result is best preserved quantitatively rather than simplified permanently to “positive.” If a new therapy later requires a different cutoff, the original ratio or copy number can be reassessed without repeating a biopsy when the archived data are sufficient.

References

Disclaimer

MET amplification results depend strongly on assay method, cutoff, tumor type, and treatment history. This article is educational and does not replace interpretation by an oncologist and molecular pathologist who can review the original report, full biomarker profile, and current treatment standards.

RELATED ARTICLESMORE FROM AUTHOR