# EGFR exon 19 deletion

Source: https://onco.cc/biomarkers/egfr-exon-19-deletion/  
OnCo record `egfr-exon-19-deletion` (Biomarker). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

An exon 19 deletion removes a few amino acids from the EGFR kinase and leaves it switched on. With L858R it makes up about 85 percent of EGFR-mutant lung cancer and is the classic gate for osimertinib and the other EGFR inhibitors.

## Summary

In-frame deletions in exon 19 (most often E746_A750del) are the commonest sensitising EGFR mutation in lung adenocarcinoma. Every EGFR tyrosine kinase inhibitor label (osimertinib, erlotinib, gefitinib, afatinib, dacomitinib, and amivantamab with lazertinib) names 'exon 19 deletions or exon 21 L858R substitution mutations' detected by an FDA-approved test; osimertinib is also labelled as adjuvant therapy after resection and with chemoradiation in stage III disease. The cobas EGFR Mutation Test v2 (tissue and plasma), therascreen EGFR RGQ PCR, Oncomine Dx Target Test, FoundationOne CDx and Liquid CDx and Guardant360 CDx are companion diagnostics; the FDA list groups the TKIs under one device indication. Exon 19 deletions respond somewhat better to TKIs than L858R in the pooled trial data.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: EGFR ex19del; exon 19 deletion; EGFR del19; E746_A750del; EGFR exon 19 del; classical EGFR mutation
- Tags: biomarker; egfr

## Notes

- Lung cancer: present in 13 to 19% of adenocarcinomas by cohort, 14.4% of 2,653 in the largest panel series, 18.9% in East Asian disease and 16.4% in never-smoker whole genomes, with E746_A750del the commonest variant (cBioPortal). It is the more responsive of the two classical alleles: exon 19 deletion leads L858R roughly 4 to 3 in Western cohorts and trails it in East Asian disease, and responds more deeply to every generation of inhibitor. Immunohistochemistry is not acceptable for the call (Lindeman 2018).

## Sources

- TAGRISSO prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5e81b4a7-b971-45e1-9c31-29cea8c87ce7
- Rybrevant prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1466c070-9f97-4fa4-a955-6a6b59981fb8

## Connected records

- biomarkers: [EGFR C797S (and its phase with T790M)](https://onco.cc/biomarkers/egfr-c797s/), [EGFR exon 20 insertion](https://onco.cc/biomarkers/egfr-exon-20-insertion/), [EGFR L858R](https://onco.cc/biomarkers/egfr-l858r/), [EGFR T790M](https://onco.cc/biomarkers/egfr-t790m/), [HER3 expression](https://onco.cc/biomarkers/her3-expression/)
- cancers: [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/)
- drugs: [Afatinib](https://onco.cc/drugs/afatinib/), [Amivantamab](https://onco.cc/drugs/amivantamab/), [cobas EGFR Mutation Test v2](https://onco.cc/drugs/cobas-egfr-mutation-test/), [Dacomitinib](https://onco.cc/drugs/dacomitinib/), [Erlotinib](https://onco.cc/drugs/erlotinib/), [FoundationOne CDx / Liquid CDx](https://onco.cc/drugs/foundationone-cdx/), [Gefitinib](https://onco.cc/drugs/gefitinib/), [Guardant360 CDx](https://onco.cc/drugs/guardant360-cdx/), [Lazertinib](https://onco.cc/drugs/lazertinib/), [Oncomine Dx Target Test](https://onco.cc/drugs/oncomine-dx-target-test/), [Osimertinib](https://onco.cc/drugs/osimertinib/), [therascreen companion diagnostic kits (KRAS, EGFR, PIK3CA, FGFR, BRAF)](https://onco.cc/drugs/therascreen-cdx/)
- terms: [EGFR exon 19 deletion & L858R](https://onco.cc/terms/egfr-exon19-l858r/), [EGFR mutation subtypes (exon 19 deletion, L858R, exon 20 insertion, T790M)](https://onco.cc/terms/egfr-mutation-subtypes/), [Next-generation sequencing (NGS)](https://onco.cc/terms/ngs/)
- key papers: [EGFR-mutant adenocarcinomas that transform to small-cell lung cancer and other neuroendocrine carcinomas: clinical outcomes](https://onco.cc/key-papers/paper-marcoux-egfr-small-cell-transformation-outcomes-jco-2019/), [Genomic and evolutionary classification of lung cancer in never smokers](https://onco.cc/key-papers/paper-zhang-lung-cancer-never-smokers-nat-genet-2021/), [Genomic landscape of lung adenocarcinoma in East Asians](https://onco.cc/key-papers/paper-chen-east-asian-lung-adenocarcinoma-nat-genet-2020/), [Updated molecular testing guideline for the selection of lung cancer patients for treatment with targeted tyrosine kinase inhibitors](https://onco.cc/key-papers/paper-lindeman-lung-molecular-testing-guideline-jto-2018/)
- targets: [EGFR](https://onco.cc/targets/egfr/)

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