EGFR

EGFR encodes a cell-surface receptor tyrosine kinase that transmits growth and survival signals after ligand binding. In cancer, EGFR can be activated by sequence variants, amplification, overexpression, or autocrine signaling. The best-established predictive use is detection of activating EGFR mutations in NSCLC to select EGFR-directed therapy. [E1-E3]

The test must identify the specific variant rather than merely state "EGFR positive." Exon 19 deletions, exon 21 p.L858R, exon 20 insertions, uncommon sensitizing variants, and acquired resistance variants have different therapeutic implications. EGFR IHC alone should not be used to select NSCLC patients for mutation-targeted TKIs. [E2-E3]

EGFR is a transmembrane receptor that binds ligands such as EGF and transforming growth factor alpha. Ligand binding promotes receptor dimerization, kinase activation, autophosphorylation, and downstream signaling through RAS-RAF-MEK-ERK, PI3K-AKT-mTOR, JAK-STAT, and other pathways. These pathways regulate epithelial growth, survival, migration, and repair. [E1]

Activating kinase-domain mutations stabilize active receptor states or alter ATP/drug binding. Amplification and overexpression can increase signaling without the same sequence variant. Therefore, mutation, copy number, and protein expression are distinct reportable biomarker classes. [E1-E3]

Activating EGFR mutations are most clinically established in lung adenocarcinoma and related non-squamous NSCLC. EGFR amplification or the EGFRvIII deletion variant can occur in glioblastoma. EGFR overexpression and pathway activity are relevant in colorectal, head-and-neck squamous, pancreatic, and other epithelial cancers, but the biomarker used for therapy selection differs by disease. [E1-E3]

For colorectal cancer, the key negative predictors for anti-EGFR antibodies are activating RAS alterations; EGFR expression alone is insufficient. For head-and-neck cancer, anti-EGFR therapy may be used without selecting patients through the NSCLC mutation framework. [E2, E3]

EGFR testing usually does not establish that a lesion is malignant. Pathology provides the diagnosis. In NSCLC, an activating EGFR variant defines a molecular subtype with major treatment implications and can support classification of tumors with limited material. [E2]

In a patient with advanced non-squamous NSCLC, identifying an EGFR driver is especially important before initiating immunotherapy because the preferred initial treatment pathway can differ. A plasma result can accelerate molecular classification, but a negative plasma result may require tissue testing. [E2, E9]

EGFR mutation status is not a simple treatment-independent prognosis test. Outcomes are strongly influenced by stage, variant, availability and sequence of targeted therapy, CNS disease, co-mutations, and acquired resistance. Patients with a targetable driver often have distinct clinical patterns, but the result should not be converted into an individual survival estimate. [E2, E4-E8]

EGFR amplification or overexpression has variable prognostic associations across other cancers. The predictive role for a specific therapy is usually more clinically useful than a generalized prognostic statement. [E1-E3]

NSCLC with exon 19 deletions or exon 21 p.L858R is sensitive to approved EGFR TKIs. Therapy options now include osimertinib-based approaches and amivantamab plus lazertinib in specific U.S. settings. [E4-E5]

EGFR exon 20 insertion mutations are structurally diverse and less sensitive to older TKIs; approved options include amivantamab-based therapy and, after platinum chemotherapy under U.S. accelerated approval, sunvozertinib. [E6, E8]

An acquired p.T790M variant historically predicts sensitivity to third-generation osimertinib after earlier-generation TKI exposure. p.C797S and other changes may cause resistance, and their meaning depends on allelic configuration and prior drugs. [E10-E12]

Plasma ctDNA can detect an activating EGFR variant at baseline and can reveal acquired resistance changes during progression. It is useful when tissue is unsafe or insufficient, but sensitivity depends on tumor burden and shedding. A negative plasma test does not assure that the tumor is negative. [E2, E9]

Routine serial ctDNA surveillance in every treated patient is not a universal standard. At radiographic or clinical progression, tissue re-biopsy can identify histologic transformation and mechanisms not detectable in plasma, while paired plasma can improve genomic coverage. [E11-E12]

Targeted real-time PCR: rapidly detects a defined list of common variants and is often used in FDA-authorized companion diagnostics.

NGS: simultaneously assesses EGFR and other drivers, detects uncommon variants, fusions, copy number, and resistance mechanisms, and conserves limited tissue when performed as a panel. [E2]

Digital PCR: highly sensitive for selected known variants in tissue or plasma but does not discover unexpected alterations.

Sanger sequencing: may be used in some laboratories but is less sensitive in low-tumor-content samples.

IHC and FISH: assess protein expression or amplification, not the activating mutation status needed for most NSCLC TKI decisions. [E2]

A molecular report should include gene, transcript, HGVS nucleotide and protein notation, exon, variant allele fraction, specimen type, tumor content, method, analytical sensitivity, coverage limitations, and clinical classification. Examples include EGFR exon 19 deletion, p.L858R, exon 20 insertion, p.T790M, or p.C797S. [E2]

It should state whether a variant is sensitizing, resistance-associated, of uncertain significance, or not currently actionable in the specific cancer. A broad phrase such as "EGFR mutation present" is inadequate. Plasma reports should contain the negative-result caveat and recommend tissue testing when clinically appropriate. [E2, E9]

An activating EGFR mutation can indicate that the tumor depends on EGFR signaling and may respond to a matched drug. It does not guarantee response, and co-alterations or disease sites may affect duration of benefit. [E2-E5]

An EGFR variant of uncertain significance should not automatically trigger targeted therapy. Protein overexpression, amplification, and kinase-domain mutations must be interpreted under separate evidence frameworks. [E1-E3]

Small biopsies, low tumor fraction, necrosis, DNA damage, assay coverage gaps, and variant nomenclature can cause false-negative or ambiguous results. Some PCR panels do not cover rare variants. [E2]

Plasma assays can be falsely negative when disease sheds little DNA, including some intrathoracic or CNS-predominant patterns. Conversely, uncommon findings require review for technical artifact or non-tumor origin. [E9]

An assay may detect a variant but lack evidence for a particular drug, stage, or line of therapy. Regulatory authorization and evidence can differ across countries. [E4-E9]

On-target resistance: p.T790M reduces sensitivity to earlier TKIs; p.C797S interferes with covalent binding of third-generation inhibitors; other kinase-domain substitutions can alter drug binding. [E10-E12]

Bypass signaling: MET amplification, ERBB2 amplification, RAS-MAPK or PI3K-pathway activation, and acquired fusions can restore downstream signaling. [E11-E12]

Phenotypic change: epithelial-to-mesenchymal transition and transformation to small-cell or squamous histology can occur. Transformation requires tissue confirmation because plasma sequencing alone does not show morphology. [E11-E12]

Heterogeneity: multiple resistance mechanisms may coexist in different tumor sites. This is a major reason paired tissue and plasma reassessment can be informative at progression. [E11-E12]

First-generation reversible TKIs: gefitinib and erlotinib.

Second-generation irreversible pan-ERBB TKIs: afatinib and dacomitinib.

Third-generation mutant-selective TKI: osimertinib, including early-stage, locally advanced, and metastatic uses under specific labels.

EGFR-MET bispecific antibody strategies: amivantamab, including combinations with chemotherapy or lazertinib for specified EGFR variants. [E4, E6]

Exon 20-directed kinase inhibitors: sunvozertinib under U.S. accelerated approval after platinum therapy. [E8]

Post-EGFR antibody-drug conjugate: datopotamab deruxtecan has a U.S. accelerated indication after prior EGFR-directed therapy and platinum chemotherapy; it targets TROP2 rather than EGFR itself. [E7]

Combination first-line therapy: the U.S. FDA approved amivantamab plus lazertinib in 2024 for first-line locally advanced or metastatic NSCLC with exon 19 deletion or p.L858R. Research is testing whether upfront combinations delay heterogeneous resistance compared with single-agent TKI. [E4]

Exon 20 options expanded: first-line amivantamab plus chemotherapy received U.S. approval in 2024, and sunvozertinib received accelerated approval in July 2025 after platinum therapy. [E6, E8]

Treatment after EGFR-TKI resistance is diversifying: datopotamab deruxtecan received U.S. accelerated approval in June 2025 after prior EGFR-directed and platinum treatment. Studies are integrating tissue, plasma, proteomics, and histology to match post-osimertinib therapy. [E7]

Current research priorities: fourth-generation inhibitors for C797S and compound variants, CNS-penetrant agents, resistance-adaptive combinations, and ctDNA-informed treatment switching. These approaches remain trial dependent unless covered by a current regulatory label. [E11-E12]

Regulatory statements describe U.S. FDA indications and should be checked against the current label for the user's country or region.