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Two different questions: the tumour and inherited risk
Tumour testing asks what biological changes are present in the cancer and whether they can help guide care. These are often acquired changes in the cancer cells. Inherited, or germline, testing asks whether you were born with a genetic change that increases cancer risk. This can have implications for relatives as well as for your own care.
The tests can overlap, but one is not a substitute for the other. A finding in tumour tissue may prompt a separate inherited-risk assessment. “Genetic” on a report does not automatically mean the change runs in your family.
Molecular diagnostics and biomarkers
Biomarkers are measurable features that may help classify a cancer, estimate aspects of its behaviour or guide treatment. Testing can examine proteins, DNA or RNA. The right panel depends on the cancer type, stage and clinical decision; a larger test is not automatically more useful.
Examples include hormone receptors and HER2 in relevant breast cancers, selected gene changes in lung cancer, and mismatch-repair or microsatellite-instability testing in appropriate settings. Each result needs cancer-specific interpretation. A marker associated with a drug in one disease does not guarantee that the same drug is suitable for another.
IHC, PCR, FISH and next-generation sequencing
- IHC: detects selected proteins in cells; it can contribute to diagnosis and treatment selection.
- PCR-based tests: look for specified genetic targets. The particular method depends on the question and whether DNA or RNA is being assessed.
- In-situ hybridisation, including FISH: can identify selected gene or chromosome changes within cells.
- Next-generation sequencing (NGS): examines multiple genetic regions together. Panels differ in the genes and kinds of changes they detect; the name NGS alone does not describe a test’s full scope.
Which sample is used?
An existing biopsy or surgery specimen may provide enough tissue, avoiding a fresh procedure. The laboratory assesses the quality of the sample and the amount of tumour present. If material is insufficient, the team may consider a new biopsy, a different sample or a suitable blood-based test.
Ask which result is needed before treatment begins and which tests can proceed alongside other planning. Do not delay urgent care or request repeat sampling without discussing the balance of benefit, safety and timing with your doctor.
Liquid biopsy: useful, but not a universal replacement
A liquid biopsy can look for tumour-derived material, such as circulating tumour DNA, in blood. In selected settings it may help find treatment-relevant changes when tissue is difficult to obtain, or investigate resistance after treatment.
A negative result does not exclude cancer or a targetable change: some tumours release little detectable DNA. A tissue test may still be needed. Blood-based molecular profiling generally cannot replace the microscopic assessment needed to establish a new diagnosis. Tests for residual disease or early detection have specific indications and limitations; they are not interchangeable with routine treatment-selection tests.
Understanding your molecular test results
A result may identify an established treatment option, suggest a clinical trial, indicate that a treatment is unlikely to work or reveal no useful target. A finding may be uncertain or lack a suitable treatment in your setting. Even a well-established biomarker does not guarantee response.
Your oncologist considers the strength of evidence, your diagnosis, prior treatment and general health. Cancer biology can change over time; repeat testing may sometimes be useful when disease returns or progresses. This is different from routinely repeating an inherited genetic test.
Inherited genetic testing and counselling
Inherited-risk assessment considers your own cancer history, cancer types and ages in relatives, and any known family variant. Some diagnoses warrant testing even without a striking family history. Inherited genetic testing examines DNA from your normal (non-cancer) cells, rather than cancer cells, usually using a blood or saliva sample. It should be accompanied by an informed discussion about what the results could mean.
A pathogenic or likely pathogenic variant may guide screening, risk reduction, treatment in some settings and testing of relatives. A negative result may be reassuring if a known family variant has been excluded, but can be uninformative when the cause of a family pattern is unknown. Follow-up may still depend on personal and family history.
A variant of uncertain significance (VUS) is not a confirmed harmful change. It should not by itself drive preventive surgery or testing relatives as though a familial cancer risk had been established. Ask how future reclassification will be communicated.
Questions to ask before testing
- Is this a tumour test, inherited-risk test, or both?
- What decision could the result change, and is there an alternative test?
- Can the existing tissue be used? When are results expected?
- Could the result suggest something relevant to relatives, and who will provide genetic counselling?
- How will my sample and information be stored, shared and used?
- Who will explain a negative or uncertain result, and what follow-up is needed?
Continue exploring
Arranging investigations through CTI
Contact CTI to coordinate the appropriate investigation with the hospital team. Confirm the procedure, preparation and location before travelling; specialised tests may involve another department or a referral laboratory.
