Biomarker tests analyze the genetic makeup and protein characteristics of a lung tumor to match each patient with the treatment most likely to work. In non-small cell lung cancer (NSCLC), which accounts for roughly 85% of lung cancers, at least ten distinct genetic alterations now have corresponding targeted therapies. The result is a treatment plan built around a tumor’s biology rather than a one-size-fits-all chemotherapy regimen.
What Biomarker Testing Looks For
When a lung cancer diagnosis is confirmed, the next step is profiling the tumor’s molecular features. Testing covers a panel of driver mutations and genetic fusions: EGFR, ALK, ROS1, BRAF, MET, RET, NTRK, NRG, KRAS, and ERBB2. Each of these represents a specific genetic error that fuels the cancer’s growth. If one is found, your oncologist can often prescribe a drug designed to block that exact mechanism.
Beyond genetic mutations, testing also measures PD-L1 expression, a protein on the surface of tumor cells that helps cancer hide from the immune system. The level of PD-L1 expression directly determines whether immunotherapy alone is an option or whether it needs to be combined with chemotherapy.
How Genetic Results Shape Drug Choices
The clearest example is EGFR mutations. Patients with EGFR-driven tumors who receive a matched targeted therapy have a median progression-free survival of 9 to 13 months and overall survival exceeding 24 to 30 months, based on data from six major clinical trials. When tumors develop resistance to earlier EGFR drugs, a next-generation option (osimertinib) has shown a median progression-free survival of about 10.4 months compared to standard chemotherapy.
ALK and ROS1 gene fusions steer treatment toward a different class of drugs. Crizotinib was one of the first therapies approved for both ALK and ROS1 rearrangements, with newer options like ceritinib also available for ALK-positive patients. BRAF V600E mutations, found in a small percentage of lung cancers, are treated with inhibitors originally developed for melanoma. In melanoma trials that led to approval, the combination of dabrafenib and trametinib dramatically reduced the risk of disease progression compared to older chemotherapy.
Rarer Mutations Still Matter
MET exon 14 skipping mutations occur in about 3 to 4% of lung adenocarcinomas and 1 to 2% of other NSCLC types, including squamous and sarcomatoid histologies. Two targeted drugs, capmatinib and tepotinib, gained regulatory approval based on the GEOMETRY mono-1 and VISION trials. A third option, savolitinib, has also shown effectiveness in both first- and second-line treatment, including in patients with the particularly aggressive sarcomatoid subtype.
NTRK fusions are even rarer but equally important to detect. When present, they open the door to a specific class of inhibitors that work across many cancer types, not just lung cancer. This is why comprehensive testing matters: skipping the panel means potentially missing a treatable target that affects only a few percent of patients.
PD-L1 Levels and Immunotherapy Decisions
PD-L1 testing uses two key cutoffs: 1% and 50%. Tumors with PD-L1 expression on 50% or more of their cells are eligible for immunotherapy drugs like pembrolizumab, atezolizumab, or cemiplimab as a standalone treatment. This threshold was first established in the KEYNOTE-001 trial and has since been validated across multiple studies.
For patients with PD-L1 expression between 1% and 49%, an FDA pooled analysis found that combining chemotherapy with immunotherapy produced better outcomes than immunotherapy alone. When PD-L1 expression is very low or absent, chemotherapy combined with immunotherapy is the typical approach. In all cases, if the tumor also harbors a targetable driver mutation like EGFR or ALK, the targeted therapy generally takes priority over immunotherapy.
How the Testing Actually Works
Biomarker testing requires tumor tissue or a blood sample. The gold standard is next-generation sequencing (NGS), which screens for dozens of genetic alterations simultaneously from a single tissue sample. This is more efficient than running individual tests one mutation at a time, which would consume more tissue and take longer.
Getting enough tissue is a genuine challenge. For a core-needle biopsy of the lung or a metastatic site, doctors typically perform at least two needle passes with an 18- to 20-gauge needle, sometimes up to six to maximize the amount of tissue collected. For bronchoscopy-based biopsies, at least five forceps biopsies are recommended, with additional passes considered to ensure there’s enough material for the full testing panel. The tumor sample needs to contain at least 10% cancer cells to minimize the risk of a false-negative result.
Pathology labs use tissue-sparing techniques like the “one biopsy per block” approach and small-sample cutting protocols to preserve as much material as possible for molecular testing. Even so, some samples are too small or degraded to yield results.
When Tissue Isn’t Available: Liquid Biopsy
Liquid biopsy offers an alternative by detecting fragments of tumor DNA circulating in the bloodstream. The key advantages are practical: it requires only a blood draw, it can be repeated over time to track how a tumor evolves, and it avoids the risks of an invasive tissue biopsy. A “liquid-first” strategy also tends to shorten the time between diagnosis and treatment, and it makes comprehensive molecular testing possible for patients whose tumors are difficult or dangerous to biopsy.
The tradeoff is sensitivity. Some tumors shed very little DNA into the blood, meaning a liquid biopsy can miss actionable mutations. In one Dutch study, 3.4% of patients had treatable genetic alterations detected only on tissue biopsy after a negative liquid biopsy. For this reason, a negative liquid biopsy result is typically followed up with tissue testing when feasible. Other barriers to wider adoption include limited standardization across labs, extra costs, and the fact that many oncology centers are still building experience with the technology.
What Happens Without Testing
Patients who skip biomarker testing or receive incomplete panels default to standard chemotherapy, sometimes combined with immunotherapy. This may work, but it means potentially missing a targeted therapy that could produce better outcomes with fewer side effects. Targeted drugs tend to be more tolerable than traditional chemotherapy because they attack cancer-specific vulnerabilities rather than broadly killing dividing cells.
The gap is especially significant for patients with driver mutations. EGFR-positive patients, for instance, respond poorly to immunotherapy alone. Without knowing the mutation exists, a patient could receive an ineffective treatment while a highly effective option sits unused. Current guidelines recommend comprehensive molecular profiling for all patients with advanced NSCLC before starting first-line treatment, regardless of age, smoking history, or tumor subtype.
Timing and Practical Considerations
One of the biggest frustrations patients face is the wait for results. NGS panels can take one to three weeks depending on the lab, and delays in getting adequate tissue can extend that timeline. Some oncologists start treatment with chemotherapy while waiting for results, then switch to a targeted therapy once the profile comes back. Others prefer to wait for results before beginning any treatment, particularly if the patient’s condition is stable enough to allow it.
If you’re newly diagnosed with NSCLC, the most important practical step is confirming that your oncology team has ordered a comprehensive panel covering all known actionable mutations, not just one or two. Partial testing is still common at some centers, and it can mean the difference between receiving a precisely matched therapy and a generic regimen that doesn’t account for your tumor’s biology.