Solid Tumor NGS Panel Test: Cancer Mutations, Fusions, and Treatment Results

A solid tumor next-generation sequencing panel examines many cancer-related genes at the same time. It can detect mutations, small insertions or deletions, copy-number changes, and—when the assay includes suitable RNA or structural-variant methods—gene fusions and splice alterations. The goal may be to confirm a diagnosis, identify a treatment target, find a resistance mechanism, determine eligibility for a clinical trial, or calculate broader biomarkers such as microsatellite instability and tumor mutational burden.

The test is usually performed on formalin-fixed tumor tissue from a biopsy or operation. Some laboratories also offer plasma circulating tumor DNA testing when tissue is unavailable or a rapid result is needed. Panel size, genes, specimen requirements, and reported biomarkers differ substantially. A “negative” report can mean that no relevant alteration was found, but it can also reflect low tumor content, degraded nucleic acid, limited gene coverage, or a fusion method that was not sensitive for the alteration. Results must therefore be read with the pathology diagnosis, cancer type, treatment history, assay description, and current drug evidence.

• One NGS panel can assess many mutation types while conserving limited tumor tissue.
• DNA and RNA analysis are complementary; RNA often improves detection of clinically important fusions.
• An actionable alteration is meaningful only in the context of cancer type, therapy availability, and evidence level.
• A negative plasma test does not rule out a tumor alteration because some cancers release little DNA into blood.
• Tumor testing can reveal a possible inherited variant that needs confirmation with a separate normal sample.

Table of Contents

• What a Solid Tumor NGS Panel Measures
• Who May Benefit and When to Test
• Tissue, Sample, and Laboratory Methods
• Mutations, Fusions, and Biomarkers
• How to Read the Report
• Matching Results to Treatment
• Repeat Testing and Liquid Biopsy
• Limitations, Germline Findings, and Next Steps

What a Solid Tumor NGS Panel Measures

Next-generation sequencing, or NGS, reads millions of DNA or RNA fragments in parallel. A solid tumor panel focuses on genes and genomic regions known to matter in cancer. Unlike a single-gene test, it can evaluate multiple potential drivers from a small amount of tissue and may reduce the need for sequential testing.

A panel can be focused, covering dozens of genes, or comprehensive, covering hundreds. The number alone does not determine quality. A smaller assay may provide excellent depth and rapid turnaround for established targets in one cancer type. A larger assay may be more useful for a rare tumor, an advanced cancer with many possible targets, or a clinical-trial search.

Depending on the design, an NGS panel may assess:

• Single-nucleotide variants, such as an activating substitution in a kinase gene.
• Small insertions and deletions, including changes that shift the reading frame.
• Copy-number gains and amplifications, which can increase the number of copies of an oncogene.
• Copy-number losses, including deletion of tumor-suppressor genes.
• Gene fusions and rearrangements, in which parts of two genes join and create an abnormal driver.
• Splice alterations, such as exon-skipping events.
• Genomic signatures, including microsatellite instability, tumor mutational burden, and sometimes homologous recombination deficiency.

Not every panel detects every category. A DNA-only test may identify many mutations and copy-number changes but can miss fusions with large or unusual introns. RNA sequencing reads the expressed transcript and can reveal the actual fusion junction, but RNA is more vulnerable to degradation in old or poorly handled tissue. Some laboratories combine DNA and RNA to obtain broader coverage.

The panel does not sequence every cell in the body. Tissue testing analyzes a mixture of cancer cells, normal stromal cells, immune cells, blood vessels, and sometimes necrosis. The proportion of tumor affects sensitivity. A mutation present in only one subclone may be below the detection limit.

Most changes reported from a tumor are somatic, meaning they arose in the cancer. A tumor result does not automatically show what is inherited. Some variants—especially in genes such as BRCA1, BRCA2, PALB2, mismatch-repair genes, TP53, or APC—can be either somatic or germline. A separate constitutional sample is needed when hereditary risk is suspected.

The test can support several clinical questions. A driver alteration may predict sensitivity to targeted therapy. A resistance alteration may explain why a drug stopped working. A molecular signature may support immunotherapy. A characteristic fusion may resolve an uncertain sarcoma or brain-tumor diagnosis. In some cancers, molecular features are now part of the formal pathologic classification.

Who May Benefit and When to Test

NGS is most established for advanced or metastatic solid tumors when multiple genomic biomarkers can affect standard treatment or clinical-trial eligibility. It is also used earlier in selected cancers when a result influences adjuvant therapy, surgery, prognosis, or diagnosis.

Common reasons to order a panel include:

• A cancer type with several guideline-recommended biomarkers, such as advanced non-small cell lung cancer.
• Metastatic disease for which tumor-agnostic biomarkers or rare targets could open treatment options.
• A rare cancer with limited standard therapies.
• An unusual pathology diagnosis that may be clarified by a defining mutation or fusion.
• Progression on targeted therapy, when the team is looking for an acquired resistance mechanism.
• Insufficient tissue for multiple sequential single-gene tests.
• Consideration of a genotype-matched clinical trial.
• A tumor result that may help determine whether dedicated germline testing is warranted.

Testing has less value when the result cannot change management, systemic treatment is not feasible, or a focused test already answers the question. The decision should consider turnaround time, tissue, expected actionability, cost, and the patient’s goals.

Timing matters. Testing at initial diagnosis may preserve options and prevent delay when treatment decisions are urgent. In advanced cancers, it is often preferable to order testing while the patient remains clinically able to receive another therapy. Waiting until all standard treatment has failed can leave too little time to obtain tissue, complete sequencing, secure insurance authorization, and enroll in a trial.

For some early-stage tumors, broad NGS is not routine. The clinically validated biomarkers may be limited to one protein stain, one mutation, or one focused assay. More testing is not always better; it can generate uncertain findings without improving care.

The ordering clinician should define the question in advance. Is the priority standard-of-care treatment, diagnostic classification, prognostic information, resistance, trial matching, or hereditary risk? The answer influences the choice between a focused panel, comprehensive genomic profiling, RNA fusion assay, immunohistochemistry, fluorescence in situ hybridization, PCR, methylation profiling, or a combination.

Pathology review is essential before ordering. A pathologist confirms that the specimen contains the intended tumor, marks an area for extraction, estimates tumor percentage, and identifies factors such as necrosis or decalcification that may reduce quality. Tissue stewardship is especially important in small lung, pancreatic, and bone biopsies.

Consent practices differ. Patients should understand that testing may not find a target, an identified target may not have an available drug, off-label treatment may not be covered, and a possible inherited finding may affect relatives. The report is a snapshot of the tumor at one time and one site.

Tissue, Sample, and Laboratory Methods

Most solid tumor panels use formalin-fixed, paraffin-embedded tissue. The laboratory may cut unstained slides or receive a tissue block. Fresh or frozen tissue, cytology cell blocks, fine-needle aspirates, pleural fluid, or other specimens may also be accepted if the assay is validated for them.

Preanalytic quality strongly affects the result. Delayed fixation can damage nucleic acids, while excessive formalin exposure can create artifacts. Acid decalcification of bone specimens can severely degrade DNA and RNA. A specimen with abundant necrosis or very few tumor cells may fail or produce a false-negative result.

The pathologist often performs macrodissection to enrich tumor cells. This means scraping or cutting the marked tumor area away from surrounding normal tissue before extraction. Enrichment improves sensitivity but cannot completely remove non-tumor cells.

The laboratory then extracts DNA, RNA, or both and measures quantity and quality. Sequencing libraries are prepared using one of several approaches:

• Amplicon-based panels amplify selected regions efficiently and can work with small inputs, but primer design may limit structural-variant detection.
• Hybrid-capture panels use probes to pull down larger genomic regions and often support broad variant, copy-number, and rearrangement analysis.
• RNA fusion panels may use anchored multiplex PCR or hybrid capture to detect known and novel partners.
• Matched tumor-normal testing sequences both the tumor and a normal sample, helping distinguish somatic from germline variants and improving some analyses.
• Tumor-only testing is common and less resource intensive, but germline filtering and TMB calculation can be more difficult.

Key quality metrics include sequencing depth, uniformity of coverage, tumor fraction, read quality, and limit of detection. The report should state whether the sample passed. A technically completed assay can still have reduced sensitivity in a low-purity specimen.

Turnaround commonly ranges from about one to four weeks, depending on specimen retrieval, laboratory workflow, assay breadth, and whether RNA testing or confirmatory studies are needed. A result that arrives after a treatment decision may still help with the next line of care, but urgent cases may require faster single-marker testing in parallel.

A panel’s gene list should be reviewed rather than inferred from its commercial name. Coverage can differ by exon and alteration type. A gene may be listed for point mutations but not fusions or copy-number changes. Some reports include only variants considered clinically relevant; others list a broader set.

Orthogonal confirmation may be recommended for an unexpected or borderline result. FISH, immunohistochemistry, PCR, or another sequencing method can resolve a low-level fusion, amplification, or technically challenging variant. Confirmation is especially important when one result would drive a major treatment decision and the finding is inconsistent with the tumor’s biology.

Mutations, Fusions, and Biomarkers

A panel report can contain several types of findings, each with different clinical meaning.

Driver mutations help the cancer grow and may be targetable. The same gene can have both actionable and non-actionable variants. For example, a drug may be validated for one hotspot but not for every alteration in that gene.

Tumor-suppressor loss can support diagnosis or identify a pathway vulnerability, but loss-of-function results are not always directly druggable. A single mutation may not prove complete loss if the second copy remains functional.

Copy-number amplification can create high oncogene expression. Calling amplification is sensitive to tumor purity and ploidy. A modest copy-number gain is not necessarily equivalent to high-level amplification or protein overexpression.

Gene fusions can create constitutively active kinases or define tumor entities. DNA panels may detect rearrangement breakpoints, while RNA confirms an expressed fusion transcript. An isolated rearrangement of uncertain function should not automatically be treated as an oncogenic fusion. The reading frame, retained domains, partner, expression, and known evidence matter.

Microsatellite instability and mismatch-repair deficiency reflect impaired DNA repair and can support immunotherapy eligibility in selected settings. NGS-based MSI must be validated for the tumor type and sample. Immunohistochemistry or PCR may be used as complementary tests.

Tumor mutational burden estimates the number of somatic mutations per megabase. Panel size, germline filtering, specimen quality, and bioinformatics alter the value. The assay-specific threshold and indication must be considered; TMB is not a universal yes-or-no predictor.

Homologous recombination deficiency can be evaluated through pathogenic variants, genomic-scar scores, or other methods. A mutation in one repair gene is not automatically equivalent to a validated HRD-positive result in every cancer.

A report may also provide mutational signatures, viral sequences, loss of heterozygosity, genomic instability scores, or expression information. These advanced features require assay-specific validation and should not be assumed from the term “NGS panel.”

The coexisting genomic context matters. A targetable driver can be accompanied by a resistance alteration, tumor-suppressor loss, or competing pathway activation. Variant allele fraction may suggest clonality, but it is affected by tumor purity, copy number, and sampling. It should not be interpreted as a simple percentage of cancer cells without modeling.

A molecular result can also refine diagnosis. Characteristic fusions define many sarcomas, while integrated molecular classification is central in brain tumors. The final diagnosis should combine morphology, immunophenotype, and molecular data rather than allowing a single isolated alteration to override contradictory evidence.

How to Read the Report

Start with the specimen and assay. Confirm whether the test used tissue or plasma, DNA or RNA, and whether it evaluated mutations, fusions, copy number, MSI, and TMB. Note the collection date and anatomic site. A treated metastasis may differ from the original tumor.

Then review the adequacy statement. Terms such as “quantity not sufficient,” “low tumor purity,” “failed RNA quality,” or “limited sensitivity” change the meaning of a negative result. A report can be technically valid but incomplete for a specific alteration class.

Results are often organized into evidence tiers. Although terminology differs, they usually separate:

Category	What it may mean	What to check
Standard-of-care biomarker	An approved or guideline-supported therapy may apply	Tumor type, disease stage, line of therapy, and required companion test
Clinical-trial or emerging target	Evidence is promising but not established standard care	Trial eligibility, location, access, and strength of evidence
Resistance alteration	The finding may predict reduced activity of a drug	Whether resistance is validated for the exact cancer and treatment
Diagnostic or prognostic alteration	The result may classify the tumor or inform expected behavior	Correlation with pathology and other tests
VUS	Clinical significance is not established	Do not use it alone for treatment or family testing

A listed drug is not necessarily a recommendation. Reports may include therapies approved in another cancer type, preclinical evidence, case reports, or trials that are no longer open. The oncology team must verify current regulatory status and guidelines.

“Actionable” can mean different things: a standard therapy, a trial, a diagnostic implication, or a hereditary referral. Ask how the laboratory defines the term. A variant in a drug target is not actionable if it is biologically inactive, if the drug does not reach the tumor site, or if stronger evidence supports another therapy.

A VUS should not guide off-label treatment simply because it appears in a familiar gene. Variant classification can change, but most VUS findings do not become clinically actionable.

A negative result should be phrased as “no reportable alteration detected by this assay,” not “the cancer has no mutations.” Every cancer has molecular changes, but the panel may not cover them or they may be below detection.

Matching Results to Treatment

Treatment matching begins with the exact alteration and cancer type. The strongest situation is a validated biomarker linked to an approved therapy in the same disease setting. Evidence is weaker when the drug is approved only in another tumor type, supported by a small basket trial, or based on laboratory data.

The oncology team considers:

• Whether the alteration is a known oncogenic driver rather than a passenger.
• Whether it is clonal and likely to be present in most tumor cells.
• Whether the drug is approved for that cancer, stage, and line of therapy.
• Whether a companion diagnostic or confirmatory test is required.
• Prior treatments and known resistance mechanisms.
• Expected benefit compared with standard non-matched therapy.
• Toxicity, organ function, drug interactions, and patient preference.
• Access, insurance coverage, and clinical-trial availability.

Some biomarkers are tumor agnostic, meaning treatment can be considered across multiple tissue origins when the specified alteration is present. Even then, response rates and durability can differ by cancer type. Tissue-agnostic does not mean biology-independent.

A molecular tumor board can help with complex reports. It may include medical oncologists, pathologists, molecular geneticists, bioinformaticians, pharmacists, genetic counselors, radiologists, and disease specialists. The group reviews evidence, sample quality, trial options, and whether additional testing is needed.

The presence of a target does not guarantee response. Tumors are heterogeneous, and parallel pathways can sustain growth. A target may be present only in a subclone. Conversely, absence of a recognized target does not mean no effective treatment exists; standard chemotherapy, endocrine therapy, immunotherapy, radiation, surgery, or a non-genomic trial may still be appropriate.

Treatment decisions should not rely on a report generated years earlier without checking whether the tumor has evolved.

Clinical trials can provide access to emerging targeted agents, combination strategies, or rare molecular cohorts. Eligibility often requires central confirmation, measurable disease, adequate organ function, and a recent biopsy. A trial match on the laboratory report should be verified directly because enrollment status changes rapidly.

Repeat Testing and Liquid Biopsy

Repeat profiling may be useful at recurrence, metastatic progression, or acquired resistance—especially when the result could select another targeted therapy. It is not required at every progression. The decision depends on the cancer, prior driver, available drugs, tissue access, and likelihood of a new actionable mechanism.

A new tissue biopsy provides histology, tumor content, and DNA plus RNA. It can detect transformation to a different tumor phenotype, which plasma alone cannot show. The disadvantages are procedure risk, delay, cost, and sampling of only one lesion.

A liquid biopsy analyzes circulating tumor DNA in plasma. It can be faster and less invasive, sample DNA shed from several metastases, and identify resistance alterations. It is particularly useful when tissue is unsafe or inadequate.

The main limitation is sensitivity. Some tumors shed little DNA, especially with low disease volume, isolated brain disease, certain histologies, or treatment response. A negative plasma result is therefore non-informative unless the assay confirms adequate tumor fraction. Tissue testing should be considered when plasma is negative and identifying a target remains important.

Plasma assays can also detect clonal hematopoiesis—age-related mutations from blood cells rather than the cancer. Genes such as DNMT3A, TET2, ASXL1, and TP53 are common sources. Matched white-blood-cell sequencing or expert interpretation can prevent a blood-clone finding from being mistaken for a tumor target.

Fusion and copy-number detection may be less reliable in low-tumor-fraction plasma. Blood TMB and tissue TMB are related but not interchangeable. Thresholds and evidence must match the assay used.

When tissue and plasma disagree, neither should be dismissed automatically. Differences can reflect timing, tumor heterogeneity, assay design, shedding, treatment selection, or technical error. A molecular pathologist can determine whether confirmation is needed.

Limitations, Germline Findings, and Next Steps

NGS panels have analytic and clinical limits. A panel may miss variants outside covered regions, low-level subclones, complex rearrangements, epigenetic changes, whole-genome structural events, or fusions not captured by its design. Formalin damage can create false calls. Bioinformatic pipelines and reporting thresholds differ among laboratories.

The result represents the sampled tumor region at the collection time. It may not capture heterogeneity across metastases. A report cannot prove that a listed therapy will work or determine the best sequence of all available treatments.

A possible germline pathogenic variant deserves special attention. Clues include a variant near the expected heterozygous fraction, a gene associated with hereditary cancer, a young age, multiple primaries, or a suggestive family history. Tumor-only testing cannot reliably establish germline status because tumor purity and copy-number changes distort allele fraction.

Confirmation uses a validated normal specimen through a hereditary-cancer laboratory. A true germline result can affect surveillance, surgery, relatives, and reproductive planning. A negative germline result may show that the variant is confined to the tumor. Genetic counseling is appropriate before or after confirmatory testing.

Before acting on a report, ask:

• Did the assay include both DNA and RNA, and which alteration types were validated?
• Was the specimen adequate, and what was the estimated tumor percentage?
• Is the finding a standard biomarker in this exact cancer and treatment setting?
• Does another method need to confirm the result?
• Could a negative result reflect poor quality or limited coverage?
• Should tissue and plasma testing be combined or repeated at resistance?
• Does any finding suggest inherited risk?
• Would a molecular tumor board or clinical-trial service add value?

Keep the complete report and the pathology report. Molecular interpretations change as evidence and approvals evolve. Re-review can be useful when treatment options are exhausted or a variant is reclassified, but a reinterpretation cannot recover an alteration the original assay did not measure.

References

• Recommendations for the use of next-generation sequencing (NGS) for patients with advanced cancer in 2024: a report from the ESMO Precision Medicine Working Group 2024 (Guideline)
• Somatic Genomic Testing in Patients With Metastatic or Advanced Cancer: ASCO Provisional Clinical Opinion 2022 (Guideline)
• Clinical practice recommendations for the use of next-generation sequencing in patients with solid cancer: a joint report from KSMO and KSP 2024 (Guideline)
• Recommendations for the Use of Next-Generation Sequencing and the Molecular Tumor Board for Patients with Advanced Cancer: A Report from KSMO and KCSG Precision Medicine Networking Group 2022 (Guideline)
• Molecular Tumor Boards: A Consensus Statement From the International Association for the Study of Lung Cancer 2025 (Position Statement)
• ESMO Precision Oncology Working Group recommendations on the structure and quality indicators for molecular tumour boards in clinical practice 2025 (Guideline)

Disclaimer

This article provides educational information and is not a substitute for medical advice, diagnosis, or treatment. Solid tumor NGS results must be interpreted for the cancer, specimen, assay, disease stage, prior therapy, and current evidence. Decisions about targeted therapy, immunotherapy, biopsy, clinical trials, and germline confirmation should be made with oncology and pathology teams.