What Does EGFR Exon 20 Mean?

EGFR stands for epidermal growth factor receptor. It is a protein on the surface of cells. EGFR is also the name of the gene that holds the recipe for that protein. A gene is written in sections. Each coding section is called an exon, and they are numbered in order. Exon 20 is the twentieth one.

An exon 20 insertion means extra genetic letters have been added in that section. Your report may print it as EGFR exon 20 insertion, ex20ins, or exon 20 ins. All three mean the same thing.

NCI's lung cancer treatment summary lists EGFR TKIs (tyrosine kinase inhibitors, which are pills) for patients with EGFR variants. The FDA labels name two common EGFR changes: exon 19 deletions and the exon 21 L858R substitution.

The NCI summary then lists a separate line: "EGFR-directed therapy (for patients with EGFR exon 20 insertions)," with amivantamab named under it.

So this is not a worse result or a better one. It points down a different route. Which treatment that route leads to depends on the exact result, on the setting, and on what each drug's current approval covers. The FDA label wording is the thing to check rather than the category name. Ask your team which exact insertion was found.

Amivantamab is not a pill. The FDA describes it as a bispecific antibody directed against the EGF and MET receptors. Bispecific means it targets two receptors. It is given by infusion into a vein.

The FDA first granted accelerated approval on May 21, 2021. That approval was for adults with locally advanced or metastatic non-small cell lung cancer with EGFR exon 20 insertion mutations, as detected by an FDA-approved test, whose disease had progressed on or after platinum-based chemotherapy. In the CHRYSALIS trial of 81 patients, the overall response rate was 40% (95% CI, 29%-51%). Median duration of response was 11.1 months (95% CI, 6.9-not evaluable). Overall response rate means the share of people whose tumors shrank by a set amount.

The FDA said continued approval under accelerated approval could depend on confirming trials.

On March 1, 2024, the FDA approved amivantamab with carboplatin and pemetrexed for first-line treatment of locally advanced or metastatic disease with EGFR exon 20 insertion mutations, as detected by an FDA-approved test. The FDA also granted traditional approval for people whose disease had progressed on or after platinum-based chemotherapy.

The trial was PAPILLON, with 308 patients. The measure was progression-free survival, or PFS. That is the time before a scan shows the cancer growing again. Median PFS was 11.4 months (95% CI: 9.8, 13.7) with amivantamab plus chemotherapy. It was 6.7 months (95% CI: 5.6, 7.3) with chemotherapy alone. The hazard ratio was 0.40 (95% CI: 0.30, 0.53; p-value<0.0001). The FDA said overall survival results were still immature.

A median is a midpoint, not a promise. Half the group did better than the figure and half did worse.

Mobocertinib (Exkivity) was a pill aimed at the same target. In the phase 3 EXCLAIM-2 trial, published in the Journal of Clinical Oncology in 2025, it was not better than chemotherapy as first treatment. Median PFS was 9.6 months in each arm.

Older pages and older printouts may still name it. Ask your team whether it is an option for you.

NCI says some biomarker tests check for one biomarker. Others check for many at the same time and may be called multigene tests or panel tests.

The sample can come from tumor tissue taken at biopsy or surgery. NCI says you might get a liquid biopsy, which uses a blood draw, if you can't safely get a tumor biopsy. For example, your tumor may be hard to reach with a needle.

The 2021 approval was paired with a blood-based companion diagnostic, Guardant360 CDx. NCI says a test is called a companion diagnostic if it is paired with a specific treatment.

The finding names a target. It does not give a stage, a grade, or a prognosis.

It also does not confirm that a drug will work for you. Response rates describe groups. Yours is a single case, and the trial numbers cannot be read as a personal forecast.

NCI says biomarker testing may not help if there is not enough tumor tissue in the sample, or if the test does not find a biomarker that matches an available therapy. Ask which test was used and whether the sample was enough.

Finally, a result on paper is not a plan. Fitness, other health problems, prior treatment, and your own goals all shape what happens next.

The FDA label for amivantamab warns of infusion-related reactions, lung inflammation (interstitial lung disease), severe rash, and eye problems. It lists signs of an infusion reaction as trouble breathing, flushing, fever, chills, nausea, chest discomfort, low blood pressure and vomiting.

• Call 911 or go to the nearest emergency department for severe trouble breathing, chest pain, sudden confusion or being hard to wake, black or tarry stool, blood in vomit or vomit that looks like coffee grounds, or substantial bleeding.
• Call your care team right away for new or worsening breathing symptoms, such as new cough or shortness of breath. The label says to withhold amivantamab immediately if lung inflammation is suspected.
• If you are having chemotherapy, call your care team right away, day or night, for a temperature of 100.4°F (38°C) or higher, chills, sore throat, mouth sores, burning when you urinate, or any other sign of infection, even without a fever. A normal temperature is not a reason to wait.
• Call your care team right away for worsening eye symptoms, or a severe or blistering rash.

• Which exact insertion was found, and where in exon 20 does it sit?
• Was this a tissue test or a blood test, and was the sample enough?
• Was a broad panel used, or a narrow one that checks only common spots?
• If the result is negative or unclear, would testing on another sample type add anything in my case?
• Is amivantamab an option now, or after another treatment first?
• What side effects should I plan for with an infusion drug?
• Is a clinical trial open for this specific change?

Start with Biomarker Testing, Pathology Reports, Biopsy, and Getting a Second Opinion.

• U.S. Food and Drug Administration — FDA approves amivantamab-vmjw for EGFR exon 20 insertion-mutated non-small cell lung cancer indications.
• U.S. Food and Drug Administration — FDA grants accelerated approval to amivantamab-vmjw for metastatic non-small cell lung cancer.
• FDA label — Rybrevant (amivantamab-vmjw), Warnings and Precautions.
• National Cancer Institute — Non-Small Cell Lung Cancer Treatment (PDQ) Health Professional Version.
• National Cancer Institute — Biomarker Testing for Cancer Treatment.
• PubMed (NIH) — EXCLAIM-2, first-line mobocertinib versus chemotherapy, J Clin Oncol 2025.