How to Read a Cancer Genomic & Biomarker Report: A Patient's Guide to Precision Oncology
Understanding a cancer genomic or biomarker report can feel overwhelming. A typical report may contain unfamiliar terms such as EGFR L858R, KRAS G12C, HER2 amplification, PD-L1 TPS 60%, TMB 12 mutations/Mb, MSI-high, variant allele frequency, or variant of uncertain significance.
But these results are not simply a list of mutations. They are pieces of a larger clinical picture that can help oncologists understand how a particular cancer is behaving, which treatments may be relevant, whether resistance may be developing, and whether a clinical trial may be appropriate.
This guide explains how to read a cancer genomic and biomarker report in plain language. It is designed to help patients and families understand the terminology and ask better questions—not to replace an oncologist, pathologist, genetic counselor, or molecular tumor board.
A biomarker is not a treatment recommendation by itself. Its significance depends on the cancer type, stage, clinical situation, treatment history, strength of evidence, and sometimes other biomarkers or resistance mechanisms.
Table of Contents
- What Is a Cancer Genomic or Biomarker Report?
- Why Is Biomarker Testing Important?
- What Types of Cancer Testing Are Used?
- Anatomy of a Genomic Report
- Genes, Variants and Mutations
- Common Types of Genetic Alterations
- Pathogenic, Likely Pathogenic and VUS
- What Does “Actionable” Mean?
- What Is Variant Allele Frequency?
- Somatic vs Germline Mutations
- Major Cancer Biomarkers Explained
- PD-L1
- Tumor Mutational Burden
- MSI and MMR
- HER2
- ER and PR
- ctDNA and Liquid Biopsy
- What Does a Negative Result Mean?
- Resistance Mutations
- How Biomarkers Connect to Treatment
- Biomarkers and Clinical Trials
- Example of a Fictional Genomic Report
- Questions to Ask Your Oncologist
- Important Limitations
- How SmartCancer Grades Evidence
- Frequently Asked Questions
What Is a Cancer Genomic or Biomarker Report?
A cancer genomic report summarizes molecular findings identified in a tumor or blood sample. Depending on the test, it may look for mutations, gene fusions, copy-number changes, amplifications, deletions, DNA-repair abnormalities, immune biomarkers, or other molecular characteristics.
A biomarker report is a broader term. Cancer biomarkers can include genomic findings as well as protein expression, immune markers, hormone receptors, circulating tumor DNA, and other measurable characteristics of a tumor.
For example, a report might identify:
- EGFR mutation
- KRAS mutation
- ALK or ROS1 fusion
- HER2 amplification or overexpression
- BRAF mutation
- BRCA1 or BRCA2 alteration
- MSI-high or mismatch-repair deficiency
- PD-L1 expression
- High tumor mutational burden
- ctDNA detected in blood
The important question is not simply “What mutations do I have?”
It is:
Why Is Biomarker Testing Important?
Cancer is not one disease. Even two tumors arising in the same organ can have substantially different molecular characteristics.
Modern oncology increasingly uses molecular information to divide cancers into biologically meaningful subgroups.
This is the foundation of precision oncology.
.png "Targeted Therapy for Cancer")
Cancer type → standard treatment
The precision-oncology model increasingly becomes:
Cancer type → stage → pathology → biomarkers → treatment → response → resistance → next treatment
Biomarker testing can therefore help identify:
- potentially targetable alterations;
- biomarkers associated with immunotherapy benefit;
- hereditary cancer risks that may affect family members;
- mechanisms of treatment resistance;
- eligibility for biomarker-selected clinical trials;
- molecular changes that may justify additional testing.
However, not every detected alteration has clinical significance.
What Types of Cancer Testing Are Used?
1. Tissue-based testing
A piece of the tumor obtained through biopsy or surgery can be analyzed for genetic and protein biomarkers.
2. Liquid biopsy
A blood sample can sometimes be analyzed for circulating tumor DNA (ctDNA) or other tumor-derived material.
3. Immunohistochemistry
Immunohistochemistry, or IHC, uses antibodies to detect proteins in tumor cells. HER2, ER, PR and PD-L1 are common examples, although the exact testing and scoring methods vary by cancer.
4. Fluorescence in situ hybridization
FISH can detect particular gene rearrangements or copy-number changes.
5. Next-generation sequencing
NGS can simultaneously examine many genes. Depending on the assay, testing may include DNA, RNA, or both.
6. Germline genetic testing
Germline testing looks for inherited genetic variants that are present throughout the body rather than only within the tumor.
These different tests are complementary. One test does not necessarily answer every clinically relevant question.
Anatomy of a Genomic Report
Although reports vary between laboratories, many contain several recurring sections.
Patient and specimen information
This may include the cancer diagnosis, specimen type, collection date, accession number and other identifying information.
Test methodology
The report may explain whether DNA sequencing, RNA sequencing, IHC, FISH, PCR, liquid biopsy or another technology was used.
Detected alterations
This is usually the section patients focus on first. It may list genes and specific molecular alterations.
Biomarker results
Some reports separately display results such as PD-L1, TMB, MSI/MMR or HER2.
Clinical interpretation
The laboratory may categorize findings according to their potential clinical significance.
Therapy associations
Some reports list drugs associated with a particular alteration. These lists should be interpreted carefully because the presence of a biomarker does not necessarily mean a particular therapy is appropriate for every patient.
Clinical trials
Some commercial reports identify potentially relevant clinical trials.
Limitations
This section is extremely important. It explains what the assay could and could not detect.
Genes, Variants and Mutations
A gene is a segment of DNA containing biological information.
A variant is a difference in DNA sequence.
A mutation is commonly used in cancer medicine to describe an acquired genetic alteration, although “variant” is often the more precise technical term.
For example:
KRAS G12C
means that the KRAS protein has a specific alteration involving amino-acid position 12.
Similarly:
EGFR L858R
describes a particular EGFR protein alteration.
The biological and clinical importance of a variant depends on the gene, exact alteration, cancer type and available evidence.
Common Types of Genetic Alterations
Single-nucleotide variant (SNV)
A single DNA base is changed.
Insertion
One or more DNA bases are added.
Deletion
DNA bases are removed.
Indel
A combined term for small insertions and deletions.
Amplification
A gene or genomic region is present in unusually high copy number.
Deletion / loss
A gene or genomic region may have reduced or absent copy number.
Gene fusion
Two previously separate genes become joined. Some cancers contain highly important oncogenic fusions.
Splice alteration
A variant affects how RNA is processed from DNA.
Structural variant
A larger genomic rearrangement can alter the structure of chromosomes or genes.
Pathogenic, Likely Pathogenic and VUS
Reports often classify variants according to their significance.
Pathogenic
Evidence supports that the variant has a disease-related biological effect.
Likely pathogenic
The available evidence strongly suggests biological significance, although uncertainty remains.
Variant of uncertain significance (VUS)
A VUS means that there is insufficient evidence to determine the clinical significance of the variant.
Benign / likely benign
These classifications generally indicate that the variant is not believed to have meaningful disease-causing significance.
What Does “Actionable” Mean?
Actionable is one of the most important—and most misunderstood—words in genomic medicine.
An actionable alteration generally means that there is some clinically relevant intervention, management implication, approved therapy, diagnostic implication, or clinical-trial opportunity associated with the finding.
But “actionable” does not automatically mean:
- there is a cure;
- the treatment will work;
- the treatment is approved for every cancer containing the alteration;
- the patient should receive the drug immediately.
The context matters.
A biomarker may be:
- FDA-approved / guideline-supported: strong clinical evidence and an established use in a particular setting;
- potentially actionable: evidence exists, but the clinical role may be less established;
- clinical-trial relevant: the finding may help identify an investigational treatment;
- biologically interesting: evidence exists mainly at the laboratory or mechanistic level.
What Is Variant Allele Frequency?
Variant allele frequency (VAF) describes the proportion of sequencing reads containing a particular variant.
For example, a report might show:
VAF: 32%
VAF can provide useful information, but it is not the same thing as “32% of the cancer cells have this mutation.”
VAF can be influenced by:
- tumor purity;
- copy-number changes;
- loss of heterozygosity;
- subclonal architecture;
- normal-cell DNA contamination;
- technical characteristics of the assay.
VAF therefore needs to be interpreted in context.
Somatic vs Germline Mutations
Somatic alterations
Somatic alterations arise during a person's lifetime and may be present only in cancer cells or a subset of them.
Germline alterations
Germline variants are inherited and are generally present throughout the body's cells.
This distinction matters because a tumor sequencing test can sometimes identify a finding that may warrant separate germline confirmation.
Examples of genes that can have hereditary cancer implications include:
- BRCA1
- BRCA2
- PALB2
- TP53
- MLH1
- MSH2
- MSH6
- PMS2
- APC
- other hereditary cancer-associated genes
Not every alteration in these genes is inherited. A genetic counselor or qualified clinician may be needed to determine whether germline testing is appropriate.
Major Cancer Biomarkers Explained
Different cancers use different biomarkers. Some of the most widely discussed include:
- EGFR
- ALK
- ROS1
- KRAS
- BRAF
- MET
- RET
- NTRK
- HER2
- BRCA1/2
- HRD
- MSI/MMR
- TMB
- PD-L1
- ER/PR
- ctDNA
The meaning of each biomarker depends heavily on the cancer context.
PD-L1 Explained
PD-L1 is a protein that can be expressed by tumor cells and/or cells within the tumor microenvironment.
PD-L1 testing is often used to help inform decisions about immune checkpoint inhibitors in certain cancers.
A report may use scoring systems such as:
- TPS — Tumor Proportion Score
- CPS — Combined Positive Score
These are not interchangeable.
A result such as PD-L1 TPS 60% therefore cannot be interpreted without knowing the cancer type, assay, scoring method and clinical context.
Tumor Mutational Burden
Tumor mutational burden (TMB) estimates the number of mutations identified per amount of DNA analyzed, commonly reported as mutations per megabase.
A report might state:
TMB: 12 mutations/Mb
Higher TMB can be associated with increased production of abnormal tumor-derived antigens in some settings, and TMB has been investigated as a biomarker for immunotherapy.
However, TMB is not a universal “immunotherapy score.”
Interpretation depends on the assay, cancer type, threshold used, other biomarkers and the clinical setting.
MSI and MMR
Microsatellite instability (MSI) reflects abnormalities involving repetitive DNA sequences.
Mismatch repair (MMR) is a DNA-repair system involving proteins such as MLH1, MSH2, MSH6 and PMS2.
Reports may therefore use terms such as:
- MSI-high
- MSI-low
- microsatellite stable (MSS)
- dMMR — deficient mismatch repair
- pMMR — proficient mismatch repair
MSI/MMR status can have important implications for treatment and, in some circumstances, hereditary cancer evaluation.
HER2
HER2 is a protein encoded by the ERBB2 gene.
HER2 status can be assessed using different methods, including IHC and in situ hybridization techniques.
Depending on the cancer and treatment context, reports may describe:
- HER2-positive;
- HER2-negative;
- HER2-low;
- HER2-ultralow;
- HER2 amplification;
- HER2 overexpression.
These terms are not necessarily interchangeable, and the clinical significance depends on the cancer type and testing methodology.
ER and PR
Estrogen receptor (ER) and progesterone receptor (PR) testing are particularly important in breast cancer.
These biomarkers can help determine whether hormone-directed treatment may have a role.
The report may provide the percentage of cells expressing the receptor and the intensity of staining, depending on the testing system.
As with other biomarkers, the result should be interpreted together with tumor type, stage, HER2 status and the overall clinical picture.
ctDNA and Liquid Biopsy
Circulating tumor DNA (ctDNA) consists of fragments of DNA released by tumors into the bloodstream.
Liquid biopsy can sometimes detect tumor-derived genetic alterations without obtaining a new tissue sample.
Potential applications include:
- identifying targetable alterations;
- monitoring molecular response;
- detecting emerging resistance alterations;
- evaluating minimal residual disease in selected settings;
- helping guide repeat molecular testing.
However, a negative liquid biopsy does not necessarily prove that a mutation is absent from the tumor.
Some tumors shed very little DNA into the bloodstream, and assay sensitivity varies.
When clinically important information is not detected in blood, tissue testing may still be necessary depending on the circumstances.
What Does a Negative Result Mean?
One of the most important lessons in genomic medicine is:
A test can only detect what its technology is designed and sensitive enough to detect.
A negative result can reflect:
- the alteration genuinely being absent;
- low tumor content;
- low levels of ctDNA;
- technical limitations;
- an alteration outside the genes or regions tested;
- an alteration type not captured by the assay.
This is why the report's limitations section deserves careful attention.
Resistance Mutations
One of the most important applications of genomic testing is understanding why a cancer may stop responding to a treatment.
Cancer is biologically heterogeneous. Treatment can eliminate sensitive cancer cells while allowing resistant populations to survive and expand.
This can produce acquired resistance.
Resistance may arise through:
- new mutations in the original target;
- activation of alternative signaling pathways;
- gene amplification;
- gene fusion;
- histologic or lineage transformation;
- loss of the treatment target;
- immune escape;
- changes in the tumor microenvironment.
A repeat biopsy or liquid biopsy may therefore reveal a molecular profile that differs from the original diagnosis.
This creates an important SmartCancer concept:
Diagnosis → Treatment → Response → Resistance → Reprofiling → Next Strategy
How Biomarkers Connect to Treatment
A useful way to interpret a report is to work through five questions.
Question 1: What cancer do I have?
The same biomarker can have different implications in different cancers.
Question 2: What is the stage?
Localized disease, locally advanced disease, metastatic disease and recurrent disease can require very different strategies.
Question 3: What biomarkers were detected?
Identify alterations that may have established, emerging or investigational relevance.
Question 4: What treatment have I already received?
A biomarker that initially predicts sensitivity may later become associated with resistance after treatment.
Question 5: What is the evidence level?
An FDA-approved therapy supported by clinical trials is fundamentally different from an experimental treatment supported only by laboratory evidence.
Therefore:
Biomarker ≠ Drug
More accurately:
Biomarker + Cancer Context + Evidence + Treatment History → Clinical Interpretation
Biomarkers and Clinical Trials
Genomic testing can also expand access to clinical-trial opportunities.
Modern oncology trials may select participants according to:
- a specific gene mutation;
- a gene fusion;
- HER2 expression;
- MSI/MMR status;
- PD-L1 expression;
- TMB;
- DNA-repair abnormalities;
- a particular resistance mutation;
- tumor type and biomarker combination.
Some trials are basket trials, in which patients with different cancer types are grouped according to a shared molecular alteration.
Others are umbrella trials, where patients with one cancer type are assigned to different treatment strategies according to their molecular profiles.
This is one reason comprehensive genomic testing can sometimes be useful even when an immediately actionable mutation is not found.
Example of a Fictional Genomic Report
The following is a simplified fictional example designed only to demonstrate how to read terminology.
Fictional Example: Metastatic Non-Small Cell Lung Cancer
EGFR: L858R detected
TP53: pathogenic variant detected
ALK: no alteration detected
ROS1: no alteration detected
KRAS: no clinically significant alteration detected
PD-L1: TPS 60%
TMB: 8 mutations/Mb
MSI: stable
How should this be approached?
EGFR L858R is the first finding that deserves attention because it is a well-established oncogenic alteration in NSCLC and has important treatment implications in appropriate clinical settings.
TP53 may be biologically important, but detecting a TP53 alteration does not automatically mean that there is an approved TP53-targeted treatment.
PD-L1 TPS 60% provides information about PD-L1 expression, but it should not be interpreted in isolation from the EGFR result and the overall clinical context.
TMB 8 is a numerical biomarker result, but its meaning depends on the assay, threshold and clinical setting.
MSI stable indicates that the tumor was not classified as MSI-high by that test.
The important lesson is that the report is not a menu of drugs. The oncologist integrates the molecular findings with pathology, stage, symptoms, imaging, treatment history and current guidelines.
Questions to Ask Your Oncologist
Patients can take the following checklist to an oncology appointment:
- What are the most clinically important findings in my report?
- Which findings are actionable today?
- Which findings are potentially actionable but experimental?
- Is there an FDA-approved or guideline-supported treatment associated with my biomarker?
- Does the biomarker apply to my specific cancer type?
- Could any finding indicate an inherited cancer risk?
- Do I need germline genetic testing or genetic counseling?
- Is my tumor suitable for comprehensive genomic profiling?
- Would RNA sequencing add useful information?
- Should the tumor be tested for PD-L1?
- What is my TMB?
- What is my MSI/MMR status?
- Should ctDNA or liquid biopsy be considered?
- If my cancer progresses, should molecular testing be repeated?
- Could a resistance mutation explain treatment failure?
- Are there biomarker-matched clinical trials?
- What does a “negative” result mean for this particular test?
- What limitations does my assay have?
What a Genomic Report Cannot Tell You
A genomic report is powerful, but it is not a crystal ball.
It generally cannot tell you with certainty:
- exactly how long you will live;
- whether a treatment will definitely work;
- whether a cancer will definitely recur;
- whether every cancer cell contains the same mutation;
- that a detected alteration is automatically treatable;
- that a negative result means the alteration is absolutely absent;
- that an experimental therapy will work because it worked in a laboratory.
Cancer outcomes are influenced by many variables, including tumor biology, stage, treatment response, resistance, overall health, metastatic sites and the characteristics of individual patients and tumors.
How SmartCancer Grades Evidence
SmartCancer uses an evidence-oriented framework to distinguish established clinical knowledge from emerging and experimental concepts.
- E0 — Hypothesis: theoretical or mechanistic idea without meaningful human evidence.
- E1 — Preclinical: laboratory, cellular or animal evidence.
- E2 — Early human evidence: preliminary clinical or early-phase human data.
- E3 — Comparative clinical evidence: stronger evidence from comparative studies and clinical trials.
- E4 — Established clinical evidence: substantial evidence supporting clinical use in appropriate settings.
- E5 — Guideline / standard-of-care evidence: incorporated into authoritative clinical practice recommendations or established standards.
This framework is particularly important when reading a genomic report because commercial laboratory reports may list approved therapies, investigational therapies and theoretical associations in the same document.
Frequently Asked Questions
What is the difference between a genomic report and a biomarker report?
A genomic report primarily describes DNA or RNA alterations, whereas a biomarker report can include genomic findings plus protein expression, immune biomarkers, hormone receptors, ctDNA and other measurements.
Does finding a mutation mean there is a treatment?
No. Some alterations are actionable, some have emerging evidence, some are useful mainly for diagnosis or prognosis, and others have no established treatment implication.
What does VUS mean?
VUS means variant of uncertain significance. There is not enough evidence to determine its clinical significance confidently. A VUS should not automatically be treated as a disease-causing or treatment-directing mutation.
What does VAF mean?
Variant allele frequency describes the proportion of sequencing reads containing a particular variant. It should not automatically be interpreted as the percentage of tumor cells carrying the mutation.
Can a blood test replace a tumor biopsy?
Not always. Liquid biopsy can be extremely useful, but sensitivity depends on tumor shedding, assay characteristics and the specific alteration. A tissue biopsy may still be necessary.
What does “no mutation detected” mean?
It means the tested assay did not detect the specified alteration. It does not necessarily prove that the alteration is absent from every cancer cell.
Can genomic testing predict my prognosis?
Some biomarkers have prognostic associations, but genomic testing alone generally cannot predict an individual patient's outcome with certainty.
Why might genomic testing be repeated?
Cancers can evolve during treatment. A new biopsy or liquid biopsy may reveal molecular changes associated with treatment resistance or progression.
What is precision oncology?
Precision oncology uses information about a patient's cancer—including pathology, molecular biomarkers and treatment history—to help select and sequence appropriate diagnostic and therapeutic strategies.
Should every cancer patient have comprehensive genomic testing?
Not necessarily. The value of testing depends on cancer type, stage, treatment setting, available tissue, clinical guidelines and the likelihood that the results could affect management. Discuss testing with the treating oncology team.
From a Genomic Report to a Cancer Treatment Strategy
A cancer genomic report is best understood as one layer of a larger oncology decision system.
The modern cancer journey can be visualized as:
↓
Pathology
↓
Stage
↓
Biomarkers & Genomics
↓
Treatment
↓
Response Monitoring
↓
Resistance
↓
Repeat Profiling
↓
Next Treatment / Clinical Trial
This is the central idea behind the SmartCancer Oncology Knowledge Graph: cancer information becomes more useful when individual facts are connected rather than presented as isolated articles.
Explore the SmartCancer Precision Oncology Knowledge Graph
- Cancer Biomarkers Explained
- PD-L1 Explained
- Tumor Mutational Burden (TMB) Explained
- SmartCancer Oncology Knowledge Graph
- Cancer Clinical Trials
- The New Blueprint for Cancer Treatment
Note: Replace any internal-link URLs above if the corresponding SmartCancer pages use different final URLs.
Medical Disclaimer
This article is for educational and informational purposes only and is not medical advice. A cancer genomic or biomarker report should be interpreted by appropriately qualified healthcare professionals in the context of the patient's diagnosis, pathology, stage, treatment history and overall health. Do not start, stop or change cancer treatment based solely on information in this article or on an automated interpretation of a genomic report.
Article Information
Publisher: SmartCancer
Topic: Cancer Genomics, Biomarkers & Precision Oncology
Audience: Cancer patients, caregivers, families and health professionals seeking patient-friendly explanations
Last reviewed: August 2026
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