Medical Oncologist
Biomarker & Molecular Testing
Do I Need Genetic Testing — Before Starting Targeted Therapy?
The fear that testing will delay your treatment is real — but starting a targeted drug without knowing whether your tumour carries the matching gene change is what causes the longer delay. This page explains what testing is done, what each type looks for, and what happens if no match is found.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed August 2026
- Testing is not optional for most — For the majority of approved targeted therapies, there is no indication for use without a confirmed gene change first.
- A negative result is still useful — Finding no match tells your oncologist which treatment does fit. It is not a dead end.
- Skipping testing wastes more time — Starting the wrong drug, then stopping when results arrive, delays the right treatment by weeks or months.
- Different tests answer different questions — Tissue testing, liquid biopsy and germline testing are not interchangeable. Your oncologist will say which applies.
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Yes, in almost all cases. Targeted therapy is designed to act on a specific gene change in your tumour. Without testing to confirm that change is present, your oncologist cannot know whether the drug will work for you. NCCN and ASCO guidance requires biomarker confirmation before most targeted therapies are prescribed.
What are the different types of genetic testing used before targeted therapy?
| Tissue molecular testing | Liquid biopsy | Germline testing | |
|---|---|---|---|
| What is analysed | DNA extracted from your tumour biopsy sample | Tumour DNA fragments shed into your blood | DNA from your blood or saliva — inherited changes only |
| When it is used | Standard first step for most solid tumours | When a new tissue biopsy is difficult, or to track treatment response | When an inherited mutation is suspected, or for certain cancer types |
| How sample is taken | Tissue from a previous or new biopsy | A routine blood draw | A blood draw or saliva swab |
| What it tells your team | Which targeted drugs may match your tumour's mutations | Confirms or tracks specific mutations without a new tissue procedure | Whether you carry inherited mutations that affect treatment or family risk |
| Turnaround | Usually one to a few weeks; depends on the panel ordered | Often faster than tissue testing once the blood is drawn | Can take longer than tumour testing — your oncologist will advise |
What should you do before your genetic test is sent?
- Ask your oncologist which specific test is needed for your cancer type — not all panels cover the same mutations.
- Confirm whether your original biopsy block can be used. Most labs work from stored tissue, so a new biopsy may not be required.
- Ask when the sample will be sent, which laboratory is processing it, and when a result is expected.
- Find out whether testing is done in-house or at an external laboratory — this affects the timeline.
- Ask whether a liquid biopsy from a blood draw is an option if getting new tissue would be difficult.
- Write down your family history of cancer. Your oncologist may recommend germline testing alongside tumour testing.
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What happens if genetic testing finds no match for targeted therapy?
Finding no actionable mutation is a result, not a failure. It means targeted therapy is not the right fit for your tumour, and your oncologist moves to the treatment that is — which may be chemotherapy, hormonal therapy, immunotherapy, or a combination.
For some cancer types, no actionable mutation is the expected finding. Targeted therapy with a confirmed match outperforms standard treatment for patients who have that match, and performs poorly or not at all for those who do not. The test exists precisely to direct each patient toward the option most likely to help them.
A negative result also stays relevant over time. Tumours can develop new mutations, and a repeat test at progression sometimes shows a change that was not present at diagnosis — opening a targeted option that was not available before.
What else do I need to know before testing begins?
Can we skip testing and start targeted therapy now because time feels short?
Skipping testing to start faster almost always results in starting the wrong treatment, which must then be stopped when results arrive — meaning the net result is delay plus unnecessary side effects. Most oncologists will not prescribe a targeted therapy without the matching biomarker result, and NCCN and ASCO guidelines do not support its use without confirmed status. If urgency is genuine, ask whether a standard chemotherapy regimen can begin in parallel while testing runs — that is different from starting a targeted drug without a confirmed indication.
My oncologist mentioned next-generation sequencing. Is that the same as a standard gene test?
No. A standard single-gene test checks for one specific mutation at a time — useful when the mutation is highly predictable for a given cancer type. Next-generation sequencing, also called NGS or comprehensive genomic profiling, reads hundreds of genes from the same tissue sample in a single run. For several cancer types, NGS is now recommended as the first step because it finds mutations a single-gene test would miss. Ask your oncologist whether a comprehensive panel or a focused targeted test is appropriate for your cancer type and stage.
My biopsy was done over a year ago. Will old tissue still give a reliable result?
Usually yes. Most molecular tests work reliably on formalin-fixed, paraffin-embedded tissue, which is the standard way biopsy samples are stored in pathology archives. The laboratory assesses sample adequacy on arrival. If the tissue has degraded or the sample is too small, a new biopsy may be requested. Before agreeing to a repeat biopsy, ask your team whether a liquid biopsy from a blood draw could answer the same question — in some situations it can, though it does not fully substitute for tissue in an initial diagnostic setting.
Can I get testing done privately to get results faster?
Accredited private laboratories in India can sometimes return results more quickly. The requirements are that the laboratory holds NABL accreditation or an equivalent, and that the result is reviewed and interpreted by your treating oncologist rather than used to self-prescribe. Discuss the option with your oncologist first — they will specify the exact panel relevant to your cancer type so that you are not paying for a broad test that does not answer the right clinical question for your situation.
Will my insurance cover the cost of genetic testing?
Coverage varies by policy and by the specific test ordered. Comprehensive genomic profiling is less consistently reimbursed than single-gene tests, though this is changing. Before proceeding, ask the hospital's billing team to submit a pre-authorisation request to your insurer with the clinical indication clearly stated in writing. Keep copies of your oncologist's written referral and the final test report, as these are typically required for reimbursement claims. Hospital patient services teams can advise on whether any state government health scheme partially covers molecular testing in your case.
Did you know?
For several cancer types — including non-small cell lung cancer and certain colorectal and breast cancers — international guidelines from NCCN and ESMO now recommend comprehensive biomarker testing before any systemic treatment decision, not only before targeted therapy.
The same test that confirms a targeted drug match can also identify whether immunotherapy or a clinical trial is a better fit — which is one reason why testing broadly is often more efficient than testing for a single mutation.
Source: NCCN Clinical Practice Guidelines in Oncology; ESMO Precision Medicine Working Group
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Common questions
Frequently asked questions
How long does genetic testing take before I can start targeted therapy?
It depends on which test is ordered and whether your existing biopsy tissue can be used. Tissue molecular testing on a stored sample typically takes longer than a blood-based liquid biopsy, and sending samples to an external specialist laboratory adds time compared with in-house processing. Ask your oncologist when the sample is being sent and when a result is expected — having a specific date means you are not waiting without a timeline. If the wait feels unacceptable, ask whether a parallel treatment can begin while results are pending.
Which cancers always require genetic testing before targeted therapy?
Non-small cell lung cancer, breast cancer, colorectal cancer, melanoma and certain blood cancers are among those where NCCN and ASCO guidelines most consistently require biomarker confirmation before targeted therapy is prescribed. The list continues to expand as new drugs are approved with specific biomarker requirements attached to their approval. For cancers where the evidence is still developing, your oncologist will tell you whether testing is standard, recommended or optional for your specific situation and stage.
What is the difference between PD-L1 testing and genetic testing?
PD-L1 is a protein marker, not a gene mutation. PD-L1 testing measures the level of this protein on tumour cells and is used to assess eligibility for certain immunotherapy drugs — not targeted therapies. Genetic testing looks for specific mutations in your tumour's DNA. The two serve different purposes and are sometimes ordered together. Your oncologist will specify which is relevant to your cancer type and the treatment under consideration, so you do not need to work out the distinction yourself.
What is the difference between tumour testing and germline testing?
Tumour testing analyses the DNA of your cancer cells specifically — mutations that developed in that tumour but are not present in the rest of your body. Germline testing analyses DNA from your blood or saliva and looks for inherited mutations you were born with and could pass on. For most targeted therapy decisions, tumour testing is what matters. Germline testing is typically added when there is a family history of cancer or when the tumour mutation found is one known to sometimes be inherited, such as BRCA1 or BRCA2.
Can a liquid biopsy replace tissue biopsy for this testing?
For specific purposes, yes. Liquid biopsy detects tumour DNA shed into the blood and can confirm known mutations without a surgical or invasive procedure. It is particularly useful when a new tissue biopsy would be difficult, when monitoring treatment response over time, or when checking for new mutations at progression. It is not yet a complete substitute for tissue testing in most initial diagnostic situations — tissue provides more detail, and a negative liquid biopsy does not rule out a mutation. Your oncologist will advise which is appropriate.
What should I do if my oncologist has not mentioned genetic testing?
Ask directly. Say: 'Is there genetic or biomarker testing that should be done before we decide on treatment?' This is a reasonable question for any patient with a solid tumour or blood cancer being considered for systemic treatment. If your oncologist explains why it is not indicated for your specific cancer type, ask them to note that in your records. If you remain uncertain after the explanation, a second opinion from another oncologist or a molecular tumour board discussion is a legitimate and available option.