What Does an EGFR Mutation Mean?

EGFR stands for epidermal growth factor receptor. It is a protein that sits on the outside of a cell. Its job is to pass a growth message inward.

An EGFR mutation is a change in the gene that builds it. The altered receptor keeps sending that message, whether or not anything asked for it. That is the whole mechanism. It is also why a drug that blocks the receptor can work so well.

In almost every case this is a change the cancer acquired during life, so it is not something you passed on or inherited, and it does not put relatives at risk. Inherited EGFR changes have been described, but they are rare. If lung cancer runs in your family, or you have never smoked and were diagnosed young, that is worth raising with your team, because the question is settled by a separate blood test rather than by the tumour report. For the difference, see biomarker testing.

The pattern is striking, and NCI publishes the numbers.

One set of 2,142 lung adenocarcinoma specimens was analyzed for the two common changes. Exon 19 deletions and L858R were found in 52 percent of tumors from people who had never smoked. In tumors from current smokers, the figure was 6 percent. In former smokers it was 15 percent.

NCI adds the wider point. EGFR and ALK changes predominate in adenocarcinomas arising in nonsmokers. KRAS and BRAF changes are more common in smokers and former smokers. So a never-smoker with lung cancer has a real chance of a targetable result. Testing should not be skipped on the assumption that lung cancer is a smoker's disease.

This is the part people miss. "EGFR mutation" is not one answer.

The common, drug-sensitive group is exon 19 deletions and the exon 21 substitution called L858R. Those two names appear together in the FDA labels, because they behave alike.

Exon 20 insertions are the exception. They sit in a different part of the gene. They do not respond the same way. And they have their own separate approvals. A report that stops at "EGFR positive" has not answered the question that decides treatment.

Osimertinib, sold as Tagrisso, is the drug most people meet first. NCI lists four approved situations:

• After surgery to remove the cancer, to help keep it from coming back.
• For stage IIIA, IIIB or IIIC disease that surgery cannot remove, and that did not get worse during or after platinum-based chemoradiation.
• As first treatment for cancer that has spread.
• With pemetrexed and platinum chemotherapy, as first treatment for cancer that has spread.

It is also approved after another EGFR inhibitor has stopped working.

The label's amount is 80 mg once daily, with or without food, though your oncologist may prescribe less if side effects call for it. In the setting after surgery, the label sets an end point. Treatment runs until the cancer returns, until side effects become unacceptable, or for up to three years. Two warnings sit near the front of that label. One is lung inflammation, called interstitial lung disease or pneumonitis. The other is a lengthened QTc interval on the heart tracing.

Here the regimen changes entirely. The drug is an infusion rather than a pill.

Amivantamab, sold as Rybrevant, has two approvals for these tumors. It is used with carboplatin and pemetrexed as first treatment for advanced disease with an exon 20 insertion. And it is used on its own for exon 20 insertions that have progressed on or after platinum chemotherapy. Both require an FDA-approved test.

The label carries practical detail worth knowing in advance. Infusion reactions are common enough that the first dose is split across two days. The first two weeks are also given through a peripheral line, to lower that risk.

For the common mutations, there is now a second first-line option that is not osimertinib.

Lazertinib, sold as Lazcluze, is approved with amivantamab as first treatment. It applies to locally advanced or metastatic disease with an exon 19 deletion or L858R. The lazertinib amount on the label is 240 mg by mouth once daily, with or without food — again, the prescription you are given is what to follow.

One instruction on that label is unusual and worth raising directly. Blood clots occur more often with this combination. Preventive anticoagulation is recommended for the first four months. The side effects reported in 20 percent or more include rash, nail problems, infusion reactions, mouth soreness, swelling, clots, tingling, fatigue and diarrhea.

It is worth being clear about what these drugs do and do not do. NCI reports that EGFR variants strongly predict a better response rate and longer progression-free survival on EGFR inhibitors. That is a prediction about the tumor, not a promise about a person. A pill that shrinks a cancer for a long stretch is a different thing from a cure, and the label language reflects that by tying treatment to progression rather than to a finish date.

Both are usable. The lazertinib label states that patients are selected on an exon 19 deletion or L858R found in tumor or plasma specimens.

That matters when a biopsy is hard to get, or when the sample is too small for a full panel. It is fair to ask which was used. A plasma test that finds nothing does not prove the mutation is absent. See liquid biopsy and tissue biopsy.

None of these drugs works forever. The tumor eventually finds a way around the block. That is why retesting, when the cancer starts growing again, is routine rather than exceptional.

The retest is also why the order matters. These approvals are layered. Osimertinib after another EGFR inhibitor. Amivantamab after platinum chemotherapy. And combinations that shuffle the sequence again. Knowing which drug came first shapes what is left. See targeted therapy for how this class works in general.

These drugs are taken at home, so the warnings on the label become yours to watch.

• Call 911 or go to an emergency department if new breathlessness, a new cough or fever comes on quickly, or you faint, feel your heart pounding or racing, or have chest pain. Lung inflammation and a lengthened QTc are the two warnings near the front of the osimertinib label, and both can turn dangerous fast. During an amivantamab infusion, breathing trouble or facial swelling is also an emergency.
• Call your care team the same day if a cough or breathlessness is milder but clearly new for you, or a rash blisters, peels, or reaches your mouth or eyes. Do not stop or restart a tablet on your own; ask first.
• Call your care team within a day or two if you get a spreading acne-like rash, sore split skin around the nails, mouth sores, or diarrhea that will not settle. Dose changes and treatments for these work better early.

• https://www.cancer.gov/about-cancer/treatment/drugs/osimertinib
• https://www.cancer.gov/types/lung/hp/non-small-cell-lung-treatment-pdq
• https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5e81b4a7-b971-45e1-9c31-29cea8c87ce7
• https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1466c070-9f97-4fa4-a955-6a6b59981fb8
• https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c417f9ee-2027-4ed5-92ad-3c19266de16c