EGFR mutation tests detect changes in the DNA sequence of the EGFR gene in a patient’s cancer cells (from tumor tissue or circulating tumor DNA). They specifically look for known activating mutations (commonly exon 19 deletions and L858R in exon 21), as well as resistance or less common variants (e.g., T790M, exon 20 insertions), rather than measuring protein levels.

These test results indicate whether a tumor is likely driven by EGFR signaling and therefore whether it may respond to EGFR-targeted therapies (tyrosine kinase inhibitors); they are used to guide treatment selection and sometimes prognosis. Methods include targeted PCR assays, sequencing panels or NGS and liquid biopsy; results must be interpreted with other clinical and pathological information.

EGFR mutation testing uses either tumor tissue or a blood sample. Tumor tissue is obtained during a biopsy or surgery (core-needle, excisional, or fine-needle aspiration) or from existing pathology blocks (formalin‑fixed, paraffin‑embedded tissue or cytology specimens). A less invasive option is a “liquid biopsy,” which tests circulating tumor DNA (ctDNA) from a routine venous blood draw.

Samples are collected by trained clinical staff, labeled and sent to a molecular diagnostics laboratory where they are processed and analyzed. Tissue testing is generally considered the definitive source when adequate tumor material is available; blood-based tests are useful when tissue is unavailable or to monitor changes over time. Turnaround times and the exact sample requirements vary by laboratory.

A positive EGFR mutation result means your tested sample contains a change in the EGFR gene. In the context of cancer (most commonly non‑small cell lung cancer), that usually indicates the tumor is driven in part by abnormal EGFR signaling and can influence treatment choices — some EGFR variants (for example, certain exon 19 deletions and L858R) predict sensitivity to EGFR‑targeted drugs while others (for example, T790M or many exon 20 insertions) are associated with resistance or different treatment approaches. If the test is done on blood (ctDNA), detecting an EGFR mutation can indicate tumor DNA is present in circulation, but test sensitivity varies by tumor burden and timing.

Limitations: EGFR mutation testing describes the molecular characteristics of the tissue or blood tested rather than your general lifetime “cancer risk.” A negative result does not rule out cancer or other drivers, and a positive result does not by itself quantify risk of developing other cancers. Interpretations depend on mutation type, clinical context and prior treatments, so review results with your oncologist or a genetic counselor to understand what your specific EGFR result means for prognosis, monitoring and treatment options for your situation.

However, accuracy can be reduced by factors such as low tumor content in the sample, poor specimen quality, tumor heterogeneity, and the test modality used — liquid (plasma) ctDNA tests are less sensitive than tissue testing and can produce false negatives when tumor DNA is low, while rare technical errors or contamination can occasionally cause false positives. For best reliability, testing should use validated assays performed in accredited labs, be interpreted alongside pathology and clinical findings, and, when results are unexpected or from a low‑quality sample, be confirmed with repeat or orthogonal testing.

You should have EGFR testing at diagnosis to guide initial therapy; thereafter repeat molecular testing when there is clinical or radiographic progression to look for resistance mutations and guide next-line treatment. If you and your team use circulating tumor DNA (ctDNA) for active monitoring, many centers check it on the same cadence as imaging (commonly every 6–12 weeks or every imaging cycle) or sooner if symptoms change.

Routine serial EGFR testing after curative-intent treatment is not usually performed unless recurrence is suspected. Because tissue biopsy is more sensitive than liquid biopsy, a repeat tissue sample is preferred when feasible at progression; ctDNA is a useful, less invasive alternative for interim monitoring. Final frequency should be individualized—ask your oncologist to align testing timing with your treatment plan, imaging schedule, disease burden and symptoms.

No — EGFR mutation test results highlight patterns of imbalance or resilience—not medical diagnoses. They reveal molecular changes that can inform prognosis and therapy choices but must be interpreted alongside symptoms, exam findings, medical history, imaging, and other laboratory or biomarker data by a qualified clinician to establish a diagnosis and guide treatment.

EGFR "mutation levels" aren't something you usually change directly—EGFR mutations are genomic alterations in the tumor, and a test reports whether and how much mutant DNA is detected (for example in tissue or circulating tumor DNA). A decrease in mutant fraction on follow‑up testing generally reflects effective cancer treatment and reduced tumor burden rather than a direct way to "fix" the mutation itself.

To lower detectable EGFR mutation signal and improve outcomes, work with your oncologist to start or adjust evidence‑based therapy targeted to your specific EGFR alteration (common EGFR tyrosine‑kinase inhibitors include osimertinib, erlotinib, gefitinib and afatinib where appropriate), evaluate for resistance mutations (e.g., T790M, C797S) with repeat tissue or liquid biopsy if disease progresses, consider clinical trials, adhere to prescribed treatment and supportive care, and address modifiable factors (smoking cessation, comorbidity management). Avoid unproven supplements or off‑label treatments and follow regular monitoring as recommended by your care team.