Variant of unknown significance Introduction (What it is)
A Variant of unknown significance is a genetic test finding where a DNA change is detected, but its health meaning is not clear.
It is commonly reported in germline (inherited) and tumor (somatic) genetic testing used in cancer care.
It means the lab cannot confidently label the variant as harmful (pathogenic) or harmless (benign) right now.
The classification can change over time as new scientific evidence becomes available.
Why Variant of unknown significance used (Purpose / benefits)
Genetic testing is used in oncology to help answer questions about cancer risk, diagnosis, prognosis, and treatment selection. When a lab sequences genes, it often finds DNA differences compared with a reference sequence. Some differences are well understood and can be classified as pathogenic/likely pathogenic (associated with disease) or benign/likely benign (not associated with disease). A Variant of unknown significance sits in the middle—evidence is insufficient or conflicting.
Although a Variant of unknown significance can feel frustrating, the category serves an important purpose: it prevents over-interpretation. Instead of forcing a variant into a “harmful” or “harmless” box without adequate proof, the lab labels uncertainty clearly. That transparency helps clinicians avoid making high-stakes cancer decisions based on incomplete information.
In practice, Variant of unknown significance results are a byproduct of increasingly comprehensive testing (multi-gene panels, tumor sequencing, paired tumor-normal testing). The more genes and regions that are analyzed, the more rare variants are found—many of which have not yet been studied enough in large, diverse populations.
From a care-system perspective, Variant of unknown significance reporting supports:
- Accurate communication of uncertainty in genomic medicine
- Appropriate clinical decision-making, emphasizing established risk factors and evidence-based biomarkers
- Future learning, because variants may later be reclassified as more data accumulates
- Patient safety, by limiting unnecessary interventions driven by misinterpreted genetic findings
Indications (When oncology clinicians use it)
A Variant of unknown significance is not “used” as a treatment; it is a possible outcome of genetic testing. Common oncology scenarios where it may appear include:
- Germline testing to evaluate hereditary cancer risk (e.g., strong family history, early-onset cancer, multiple related cancers)
- Testing after a new cancer diagnosis to support treatment planning when inherited syndromes could influence options (varies by cancer type and stage)
- Tumor genomic profiling to look for actionable alterations (therapy targets, resistance mechanisms, or trial eligibility)
- Paired tumor-normal testing to distinguish inherited variants from tumor-acquired variants
- Evaluation of unusual tumor types, multiple primary cancers, or rare clinical patterns where genetics may help clarify diagnosis
- Cascade-related questions in families where a relative had genetic testing and a Variant of unknown significance was reported
Contraindications / when it’s NOT ideal
Because a Variant of unknown significance is uncertain by definition, there are situations where relying on it is not suitable, and other approaches may be more informative:
- Using a Variant of unknown significance as the sole reason for major risk-reducing surgery, intensive screening, or treatment escalation is generally not an evidence-based use
- Ordering broad genetic panels without a clear clinical question may increase the chance of uncertain findings that do not change care
- Testing without access to genetic counseling (or a clinician with genetics expertise) can increase misunderstanding and anxiety
- Family “predictive testing” based only on a Variant of unknown significance is often not informative, because the variant’s meaning is unresolved (the appropriate approach varies by clinician and case)
- Situations where the key decision depends on well-validated biomarkers (for example, established tumor markers or clearly actionable mutations) rather than uncertain variants
How it works (Mechanism / physiology)
A Variant of unknown significance is an interpretation category, not a drug, procedure, or device. Its “mechanism” is best understood as a laboratory and clinical classification pathway.
Clinical pathway (how a variant becomes a Variant of unknown significance)
- DNA is sequenced from blood/saliva (germline) and/or tumor tissue/blood (somatic).
- Bioinformatics identifies differences from the reference sequence (variant calling).
- The lab evaluates evidence to classify each variant using established frameworks (commonly aligned with professional guidelines such as ACMG/AMP principles, though practices can vary by lab and test type).
- If evidence is insufficient or conflicting, the lab reports the finding as a Variant of unknown significance.
What evidence is considered
Labs weigh multiple lines of evidence, for example:
- Population frequency: Is the variant common in the general population? Very common variants are less likely to cause rare hereditary cancer syndromes.
- Predicted functional impact: Does the change alter the protein in a way that is plausibly damaging (computational predictions are supportive but not definitive)?
- Published literature and case reports: Has the variant been observed in affected individuals, and does it track with disease?
- Segregation data: In families, does the variant appear consistently in relatives with the condition and not in unaffected relatives?
- Functional studies: Laboratory experiments may test whether the variant disrupts gene or protein function (availability varies by gene and variant).
- Tumor features: In some contexts, tumor characteristics (such as specific mutation patterns or protein expression) can support or weaken a hypothesis, but this is rarely definitive alone.
Onset, duration, and reversibility (what applies here)
- A Variant of unknown significance does not have an onset or duration like a therapy.
- The classification is revisable: it may later be reclassified as benign/likely benign or pathogenic/likely pathogenic when new evidence emerges.
- Reclassification timing is variable and depends on research progress, data sharing, and how often labs re-review evidence.
Variant of unknown significance Procedure overview (How it’s applied)
A Variant of unknown significance is not a procedure, but it commonly appears within a standard oncology genetics workflow. A high-level pathway often looks like this:
- Evaluation/exam: A clinician reviews the cancer diagnosis, pathology, age at diagnosis, and personal and family history.
- Imaging/biopsy/labs: Cancer workup proceeds as indicated; genetic testing is considered alongside standard diagnostic steps.
- Staging: Cancer staging is determined using established methods (varies by cancer type and stage).
- Treatment planning: The team identifies whether germline or tumor testing could clarify hereditary risk, prognosis, or therapy options.
- Testing process: Informed consent and pre-test education may occur; a sample is collected (blood, saliva, or tumor tissue).
- Result reporting: The lab report lists clinically significant findings (if present) and may include a Variant of unknown significance.
- Clinical interpretation: Clinicians integrate the report with the patient’s cancer type, pathology, and family history. Uncertain variants are typically treated as uninformative for decision-making unless and until reclassified.
- Response assessment: Treatment response is evaluated using routine oncology measures; Variant of unknown significance results usually do not serve as response markers.
- Follow-up/survivorship: Documentation, potential re-contact processes, and family-history updates may be part of ongoing care. Some labs issue amended reports if a variant is reclassified.
Types / variations
Variant of unknown significance findings vary by testing context, specimen type, and clinical goal.
Germline (inherited) Variant of unknown significance
- Found in DNA from blood or saliva.
- Often reported on hereditary cancer panels (multi-gene testing).
- May involve genes associated with cancer predisposition (examples vary widely), where the variant’s impact on gene function is unclear.
Somatic (tumor-acquired) Variant of unknown significance
- Found in tumor tissue or circulating tumor DNA (ctDNA) assays.
- May reflect a passenger change with no effect on tumor behavior, or a potentially meaningful alteration not yet well characterized.
- Can be challenging to interpret because tumors contain many genetic changes and may show heterogeneity (different clones within the tumor).
Tumor-only vs paired tumor-normal testing
- Tumor-only testing may detect variants that could be somatic or germline; uncertainty about origin can complicate interpretation.
- Paired testing compares tumor DNA with normal DNA to help clarify whether a variant is inherited or tumor-acquired, which can reduce some ambiguity (but does not eliminate Variant of unknown significance findings).
Panel size and test design
- Larger panels and broader sequencing (including non-coding regions or less-studied genes) can increase the chance of Variant of unknown significance results.
- Some tests incorporate additional data (for example, RNA analysis in select settings) that may help clarify certain variant effects, though availability varies.
Clinical setting differences
- Solid tumors: Variant of unknown significance may appear in tumor profiling or hereditary testing for breast/ovarian, colorectal, prostate, pancreatic, and other cancers (examples vary by clinic).
- Hematologic malignancies: Sequencing may identify variants with unclear significance for diagnosis or prognosis, especially when differentiating inherited predisposition from acquired changes.
- Adult vs pediatric: Pediatric oncology may involve different gene-disease relationships and a stronger focus on cancer predisposition syndromes in select cases.
Pros and cons
Pros:
- Clarifies that evidence is insufficient, reducing the risk of overconfident interpretation
- Encourages decisions based on established clinical factors and validated biomarkers
- Supports ongoing learning as databases, publications, and functional data evolve
- Can prompt careful review of family history and pathology for consistency (without assuming causality)
- Provides a documented result that can be revisited if reclassification occurs
Cons:
- Can increase anxiety because it sounds like an unresolved “maybe” result
- Often does not change treatment or screening plans, which can feel unsatisfying after testing
- May be misunderstood as “positive” or “negative” when it is neither
- Reclassification timelines are unpredictable and may never occur for some variants
- Interpretation can differ slightly among laboratories due to evidence thresholds and internal data
- Can complicate family discussions if relatives seek clear yes/no answers
Aftercare & longevity
The “aftercare” for a Variant of unknown significance is mainly about communication, documentation, and follow-up systems, rather than recovery from a medical intervention.
What can affect how the result is handled over time includes:
- Cancer type and stage: Treatment and surveillance planning are usually driven by established oncology guidelines, pathology, and staging; the impact of an uncertain variant is typically limited.
- Tumor biology and validated biomarkers: When strong predictive markers exist (for example, certain actionable mutations), they typically carry more weight than uncertain findings.
- Quality of the clinical context: Detailed personal and family history, accurate pathology, and clear testing indications make results easier to interpret responsibly.
- Whether the variant is reclassified: Reclassification depends on accumulating evidence (population data, clinical observations, functional studies) and laboratory review practices.
- Care coordination and records: Keeping test reports accessible in the medical record supports continuity if care teams change.
- Access to genetics expertise: Genetic counselors and genetics-informed clinicians can help translate uncertainty into clear, non-alarmist language.
- Survivorship and follow-ups: Ongoing oncology follow-up focuses on recurrence monitoring, late effects, and supportive care; Variant of unknown significance results may be revisited if new information emerges.
This is informational only: any specific follow-up plan varies by clinician and case.
Alternatives / comparisons
Because a Variant of unknown significance is a category of uncertainty, the most relevant “alternatives” are other result types or additional approaches that may reduce uncertainty.
Variant of unknown significance vs pathogenic/likely pathogenic
- Pathogenic/likely pathogenic variants have stronger evidence and may influence management (for example, eligibility for certain targeted therapies in select contexts, or hereditary risk counseling).
- A Variant of unknown significance generally does not provide the same level of actionability because causation is not established.
Variant of unknown significance vs benign/likely benign
- Benign/likely benign variants are considered normal human variation and are not expected to explain cancer risk or tumor behavior.
- A Variant of unknown significance cannot be treated as benign because evidence is incomplete.
Observation/active surveillance (in hereditary risk discussions)
- When genetic results are uncertain, clinicians often rely more on personal and family history and standard screening guidance. This may resemble an “observation” approach for the genetic finding itself—tracking updates rather than acting on the variant.
- The specifics of screening and surveillance vary by cancer type and individual risk profile.
Additional testing or evidence-building approaches
Depending on the scenario, the care team may consider:
- Updated or expanded testing if earlier tests were limited (benefits vary).
- Testing an affected relative (in select hereditary evaluations) to see whether a clearer pathogenic variant is present elsewhere in the family.
- Segregation studies (family studies) in certain circumstances; these can help but do not always resolve uncertainty.
- Tumor testing correlations (for germline variants) or paired tumor-normal testing to clarify origin.
- Clinical trials: Trials usually require specific eligibility criteria; a Variant of unknown significance alone is often insufficient unless paired with other qualifying findings (varies by trial).
Variant of unknown significance Common questions (FAQ)
Q: Does a Variant of unknown significance mean I have inherited cancer risk?
It means a DNA change was found, but its relationship to cancer risk is not established. It is not the same as a pathogenic mutation. Clinicians typically interpret it alongside personal and family history rather than treating it as a confirmed hereditary syndrome.
Q: Is a Variant of unknown significance the same as a “positive” genetic test?
No. A “positive” result usually refers to a pathogenic or likely pathogenic variant with evidence of disease association. A Variant of unknown significance is an indeterminate finding and is often considered non-actionable by itself.
Q: Can a Variant of unknown significance affect my cancer treatment plan?
In many cases, it does not change treatment because its meaning is uncertain. Treatment decisions are usually based on cancer type, stage, pathology, validated biomarkers, and overall health. Exceptions depend on the clinical context and evolving evidence, and vary by clinician and case.
Q: Will the Variant of unknown significance result ever change?
It can. Laboratories may reclassify variants as new data becomes available, but the timing is unpredictable and some variants remain uncertain. Some labs issue updated reports, and some healthcare systems have processes to revisit results over time.
Q: Does testing for this involve pain or anesthesia?
Genetic testing typically uses a blood draw or saliva sample, which does not require anesthesia. Tumor genetic testing uses previously collected biopsy or surgical tissue when available; obtaining new tissue, if needed, depends on the broader cancer care plan.
Q: Are there side effects or safety concerns from genetic testing?
The physical risks are usually limited to sample collection (for example, minor discomfort or bruising from a blood draw). Non-physical considerations can include stress, uncertainty, and concerns about family implications. Privacy and insurance issues vary by location and policy.
Q: How long does it take to get results and how long does the result “last”?
Turnaround time varies by laboratory, test type, and clinical setting, and no single timeframe applies. The result remains part of the medical record, but the interpretation may evolve if reclassification occurs.
Q: What does a Variant of unknown significance mean for my relatives?
Because the variant’s meaning is unclear, it often does not provide a clear yes/no answer for relatives. Family risk assessment is commonly based more on shared history and any clearly pathogenic variants identified in the family. Whether any relatives are tested and how results are used varies by clinician and case.
Q: What about fertility or pregnancy planning?
A Variant of unknown significance does not confirm an inherited cancer syndrome, so it usually cannot be used as a definitive basis for reproductive risk calculations. In some situations, genetics professionals discuss options for family planning in the context of personal and family history and any confirmed pathogenic findings.
Q: What is the cost range for testing that might report a Variant of unknown significance?
Costs vary widely based on the type of test (single-gene vs panel vs tumor sequencing), insurance coverage, and region. Financial counseling or billing support services may be available in many cancer centers to help patients understand coverage and out-of-pocket expectations.