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MET exon 14 skipping is a great example of how a cancer-driving mutation can arise not from a typo in the DNA code itself, but from a malfunction in how that code gets edited before it’s used — understanding this distinction is actually central to why it’s called “skipping” rather than just another point mutation.

The basic biology — what MET does normally

MET is a receptor kinase coded by the MET gene and is expressed on the surfaces of epithelial cells. Under normal circumstances, MET receives a signal from a growth factor called HGF (hepatocyte growth factor) and triggers downstream signaling pathways involved in cell growth, survival, and movement — important during normal tissue development and wound healing, but dangerous if left unregulated.

To keep MET signaling in check, the normal protein includes a built-in regulatory mechanism: a specific region encoded by “exon 14” of the MET gene contains instructions for a portion of the protein that gets tagged for degradation once MET has been activated long enough. This degradation tag — involving a process called ubiquitination — is essentially a built-in shut-off switch, ensuring MET signaling doesn’t run unchecked.

What “exon 14 skipping” actually means

Genes aren’t read directly from DNA into protein — there’s an intermediate step called RNA splicing, where the cell cuts out certain non-coding sections and stitches together the coding sections (exons) to build the final instructions for the protein. Normally, exon 14 is one of the pieces included in this final assembly.

In MET exon 14 skipping, a mutation — usually located near the splice sites that flank exon 14, rather than within exon 14 itself — disrupts the cell’s ability to recognize and include exon 14 during this splicing process. The cellular splicing machinery essentially skips over exon 14 entirely, producing a MET protein that is missing this regulatory segment.

This results in a protein with a missing regulatory domain that reduces its negative regulation, leading to increased downstream MET signaling. In plain terms: the cell loses its molecular “off switch” for MET, and the signal that promotes cell growth and survival keeps firing far longer and more intensely than it should — driving cancer growth.

Why this matters for lung cancer specifically

In NSCLC, MET exon 14 skipping mutation is observed in 3-4% of cases, and the incidence varies by histologic subtype — about 2% in adenocarcinoma, 6% in adenosquamous cell carcinoma, and notably higher at 13% in pulmonary sarcomatoid carcinoma. This is a relatively uncommon but well-defined “oncogenic driver” — meaning in patients who have it, this single genetic alteration is generally considered to be the primary force pushing the cancer’s growth, similar conceptually to EGFR mutations or ALK rearrangements in other NSCLC patients, but representing a distinct, separate subgroup

MET exon 14 skipping typically occurs in the absence of other driver mutations — meaning if this mutation is found, it’s usually not accompanied by EGFR, ALK, or other major drivers, reinforcing its role as the primary actionable target for that patient’s cancer.

How testing actually works

Sample types — testing can be performed on tumor tissue (from biopsy or surgical specimen) or on a blood-based liquid biopsy (plasma), similar to the dual-sample approach we discussed for FGFR3 testing in bladder cancer. If a mutation isn’t detected in a plasma specimen, testing tumor tissue is recommended if feasible — plasma testing can sometimes miss a mutation that’s present in the tumor due to limitations in how much tumor DNA sheds into the bloodstream.

Testing methodology — because exon 14 skipping results from a splicing defect rather than a simple, easily detected point mutation, the testing technology matters more than for some other mutations. The two main approaches are:

RNA-based or NGS (next-generation sequencing) panels — the FoundationOne CDx assay served as the approved companion diagnostic for capmatinib, and broader genomic panels can detect the splice-site alterations or, more directly, detect that exon 14 is actually missing from the final RNA transcript.

DNA-based panels — can detect mutations at the splice sites that cause the skipping, though this requires the panel to specifically include and properly analyze these regions, since the mutations causing skipping can occur at various positions around exon 14’s boundaries rather than in one single consistent spot.

Why detection technology genuinely matters here — a real discordance example

A documented case report described a patient whose MET exon 14 skipping was positive on one testing platform (Oncomine Dx Target Test) but negative on another (ArcherMET), despite using the same residual RNA sample — the discordant result traced back to extremely low read counts for the relevant MET exon junction on the platform that returned a negative result.

This is a genuinely important practical lesson: unlike a simple “yes/no” mutation test, exon 14 skipping detection can vary meaningfully between testing platforms due to technical differences in how each platform analyzes the relevant RNA splice junctions. Companion diagnostics validated for these drugs vary by region — in Japan, for example, ArcherMET and AmoyDx tests are used, but the Oncomine Dx Target Test is not validated as a companion diagnostic there for the same drugs that are approved in other markets using different validated tests.

The practical implication for patients

If you’ve had NSCLC genomic testing and MET exon 14 skipping wasn’t detected, but your cancer’s histology (particularly sarcomatoid features) or other clinical factors make your oncologist suspicious that this driver might still be present, it’s reasonable to ask whether a different, more sensitive testing platform — particularly one with RNA-based detection — might be worth pursuing, rather than assuming a single negative result is necessarily definitive. This is a more nuanced situation than testing for many other single-point mutations, precisely because of how exon 14 skipping arises at the RNA splicing level rather than through a simpler DNA-level change.

Why this is treated as equally important as more “famous” driver mutations

Even though MET exon 14 skipping is less commonly discussed than EGFR or ALK alterations, it functions the same way clinically: a single, well-characterized molecular driver that defines a specific patient population eligible for a specific targeted therapy (capmatinib or tepotinib), with response rates well above what’s typically seen with chemotherapy in unselected NSCLC patients. This is precisely why comprehensive genomic testing — rather than testing only for the most well-known mutations — has become standard practice in newly diagnosed metastatic NSCLC, since missing a rarer but actionable driver like this one means missing access to a substantially more effective, better-tolerated treatment option.