MET exon 14 skipping

What it is

MET exon 14 skipping is an actionable MET gene alteration found in about 3% to 4% of non-small-cell lung cancers. It is a biomarker, not a symptom or a cancer type, and its main importance is that it can make some lung cancers eligible for MET-targeted treatment. The alteration is usually written as METex14 or MET exon 14 skipping mutation, although many different DNA changes can cause the same final effect.

In this alteration, the cancer cell makes MET messenger RNA that skips exon 14, so exon 13 is joined directly to exon 15. This matters because exon 14 contains part of the MET receptor's regulatory region. When that region is lost, the MET protein is not broken down normally and signaling can stay switched on longer than it should, which can promote tumour growth.

MET exon 14 skipping is most relevant in non-small-cell lung cancer (NSCLC), especially advanced disease where broad molecular testing guides treatment choices. It tends to occur without another major driver mutation, although MET amplification can sometimes be present at the same time.

Key point	Why it matters
Found in about 3% to 4% of NSCLC	Common enough that routine molecular testing should look for it
It is an actionable biomarker	A positive result may open the door to MET inhibitor therapy
Many different DNA variants can cause it	Testing method matters because some assays can miss it

How it works

The MET gene encodes a receptor tyrosine kinase involved in cell growth, survival, movement, and tissue repair. Exon 14 codes for part of the juxtamembrane domain, a short regulatory segment that helps control receptor turnover. When exon 14 is skipped during RNA splicing, the resulting MET receptor loses an important control region.

The best-known consequence is impaired receptor degradation. Instead of being tagged and cleared in a normal way, the altered MET receptor can persist and continue sending growth signals through downstream pathways such as MAPK, PI3K/AKT, and others involved in cancer cell survival and proliferation.

A practical point is that MET exon 14 skipping is not one single mutation. Hundreds of distinct genomic changes have been described, including:

1. Splice-site substitutions
2. Small insertions or deletions near exon 14
3. Intronic variants adjacent to splice regions
4. Whole exon 14 deletions
5. Rare point mutations that mimic loss of the region

All of these can lead to the same RNA-level outcome: exon 14 is skipped.

Evidence and uses

In modern oncology, MET exon 14 skipping is used mainly as a predictive biomarker in NSCLC. If a patient's tumour has this alteration, the oncology team may consider a MET inhibitor, depending on the stage of disease, prior treatment, drug availability, and local regulatory context. This is why many lung cancer guidelines recommend comprehensive molecular profiling in advanced non-squamous NSCLC and in selected other NSCLC cases.

Evidence from clinical studies and real-world series shows that MET-targeted therapies can produce meaningful responses in patients with METex14-positive NSCLC. Response rates and duration of benefit vary across studies, drugs, and treatment lines, so the exact expected benefit should be discussed with the treating oncologist rather than assumed from one paper.

This biomarker also has diagnostic value because it helps classify the tumour's biology. In many cases, METex14 behaves like a primary oncogenic driver. Coexisting driver alterations are less common than in unselected NSCLC, though they can occur. MET amplification may be seen alongside METex14 in a subset of tumours.

For patients in India, the practical issue is access to reliable next-generation sequencing (NGS). Large cancer centres and reference laboratories increasingly offer broad DNA panels, and some also use RNA-based testing. Because targeted therapy decisions may depend on this result, it is worth asking whether the laboratory's assay is designed to detect MET exon 14 skipping well.

Diagnosis / how it's measured

MET exon 14 skipping is detected by molecular testing, not by routine imaging or standard blood tests. The sample is usually tumour tissue from a biopsy, though plasma-based liquid biopsy may sometimes be used when tissue is limited or repeat biopsy is difficult.

The main testing approaches are:

Test approach	Strengths	Limitations
DNA-based NGS	Widely available; can assess many genes at once	Some amplicon-based assays may miss certain METex14-causing variants
RNA-based NGS	Often better at directly detecting the exon-skipping event	Needs good RNA quality; not available everywhere
Liquid biopsy NGS	Useful when tissue is scarce or unsafe to obtain	A negative result may need tissue confirmation

A key challenge is that the underlying DNA changes are highly diverse. Some older or narrow amplicon-based assays may not cover enough splice-region variants, which can lead to false-negative results. One review noted that RNA-based methods have shown superior detection compared with some DNA amplicon-based methods, although well-designed hybrid-capture DNA assays can also perform well.

When reading a report, useful details include:

1. Whether the result is from tissue or plasma
2. Whether the platform used DNA, RNA, or both
3. Whether the report states MET exon 14 skipping detected or names a splice-site variant predicted to cause skipping
4. Whether other drivers or MET amplification were also found

If the clinical picture strongly suggests an actionable driver but testing is negative or inconclusive, oncologists may consider repeat biopsy, broader NGS, or RNA-based confirmation.

When to see a clinician

See an oncologist or molecular tumour board if you or your family member has newly diagnosed advanced NSCLC, recurrent lung cancer, or a pathology report showing MET exon 14 skipping. This result can affect treatment planning, so it should be reviewed before starting or changing systemic therapy when possible.

You should also ask for specialist review if:

1. The report mentions a MET splice-site variant but does not clearly say whether exon 14 skipping is predicted
2. The test was done on a small panel that may not fully assess MET alterations
3. Tissue was insufficient and only a limited test was performed
4. The cancer has progressed after prior targeted therapy and repeat molecular testing is being considered

For patients already on treatment, new symptoms such as worsening breathlessness, rapid decline in performance status, or suspected drug side effects need prompt medical attention. Treatment choice depends on the whole clinical picture, not the biomarker alone.

Limitations and open questions

Although MET exon 14 skipping is clearly actionable, several uncertainties remain. The first is testing sensitivity. Not all assays detect this alteration equally well, and false negatives can happen, especially with limited or poorly designed panels.

The second is that not every METex14-positive tumour responds the same way. Outcomes may differ based on co-mutations, presence of MET amplification, prior therapies, brain metastases, and the specific MET inhibitor used. Resistance also develops, and both on-target and off-target resistance mechanisms are being studied.

Another open question is the best sequencing of therapy relative to immunotherapy and chemotherapy. Some METex14 tumours can show PD-L1 expression, but PD-L1 alone does not reliably predict benefit, and treatment planning still needs individualised oncology input.

Finally, most evidence comes from international studies, retrospective series, and single-arm trials rather than head-to-head comparisons. That means the biomarker is clinically useful and established, but some details about the best testing strategy and best treatment sequence are still evolving.