Medical Oncologist
CION Cancer Clinics
How to ask for a drug-gene test before treatment starts | CION Cancer Clinics
You can ask your oncologist whether a drug-gene test is worth doing before your first dose. For a short list of cancer medicines, one inherited gene decides how safely your body clears the drug, and a blood test can read it in advance. This page explains when to ask, what to say, what happens if the test is not done, and why most results are normal. At CION Cancer Clinics, our team helps carriers and their families plan checks, next steps and support after a genetic result.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
17+specialists on panel
15,000+patients treated
35+centres across Telangana & AP
4.8★ / 800+Google rating
On this page
- Can I ask for a gene test before my chemotherapy starts?
- Which cancer medicines is it worth asking about?
- How do I bring it up with my oncologist?
- The terms around drug-gene testing, in plain language
- What the test can change, and what it cannot
- What this page cannot tell you
- Four worries families have about asking, and what is true
- Common questions about asking for a drug-gene test
The short answer
Can I ask for a gene test before my chemotherapy starts?
Yes. It is a reasonable request, and a good oncologist will not take offence. The test only applies to a short list of drugs, so the first thing to find out is whether your treatment plan includes one of them.
Why asking matters in India
In parts of Europe, testing before some of these drugs now happens automatically. In India it usually does not. Laboratories here do offer it, but it is often ordered only when a doctor or a family raises it. Asking early gives the result time to arrive before the first dose is given.
What you are really asking
You are not questioning the treatment plan or the doctor. You are asking whether your own body can clear the planned drug safely at the planned dose. That is a question about you. It is the kind of question oncologists are glad a family thought to raise.
The best moment to ask is the visit where the treatment plan is first explained, not the morning of the first cycle.Worth asking about
Which cancer medicines is it worth asking about?
Each of these drugs has published guidance linking it to one gene. How firmly testing is advised differs between countries.
Fluorouracil and capecitabine
The gene is DPYD. A weak version can let the drug build up and cause severe diarrhoea, mouth sores and dangerously low blood counts.
Often used in
- Bowel and stomach cancer
- Breast cancer
- Head and neck cancer
Irinotecan
The gene is UGT1A1. A common weaker version, the same one behind the harmless condition called Gilbert syndrome, can raise the chance of severe diarrhoea and a low white cell count.
Mercaptopurine and thioguanine
The genes are TPMT and NUDT15. These tablets are used in childhood leukaemia. NUDT15 differences are more common in people of Asian ancestry, which makes this pair especially relevant here.
Rasburicase
The gene is G6PD. This drug protects the kidneys when a fast-growing cancer breaks down. In someone with G6PD deficiency it can destroy red blood cells, so it is not safe to use.
Not sure whether this applies to you?
Ask an oncologistAt the planning visit
How do I bring it up with my oncologist?
Ask which drugs are in the plan
Write down the name of every medicine you are told about. Brand names differ, so ask for the generic name as well.
Ask whether any has a gene test
A simple way to say it: "Is there a gene test for any of these that should be done before the first dose?" Your oncologist will know straight away.
Ask whether there is time to wait
Some cancers need treatment to start quickly. Ask whether waiting for the result is safe, or whether a cautious first dose makes more sense.
Ask what a weak result would change
Knowing the plan in advance helps. The usual answers are a lower starting dose, closer blood tests, or a different drug.
Ask for a copy of the report
The result holds for life. Keep it with your treatment file and show it to any doctor who prescribes you a new medicine.
Words you may hear
The terms around drug-gene testing, in plain language
- Pharmacogenomics
- The study of how your genes change the way your body handles a medicine. Often shortened to drug-gene testing.
- Enzyme
- A body chemical that breaks down or clears a drug. Each enzyme is built from a gene instruction.
- Metaboliser
- How fast your body processes a drug. Reports describe you as a normal, intermediate or poor metaboliser.
- Poor metaboliser
- Your body clears the drug slowly, so a standard dose can build up and act like an overdose.
- Genotype
- The exact versions of a gene that you inherited, one from each parent. The report usually prints these as short codes.
- Germline
- Present in every cell from birth. Drug-gene tests read germline genes, which is why the result never changes.
Leave a number, we will call you
One field. No form to fill in, and no charge for the call.
Side by side
What the test can change, and what it cannot
It can change
It does not change
The starting dose of a listed drug
Whether that drug is right for your cancer
Whether a different drug is chosen instead
Your own risk of developing cancer
How closely you are watched in early cycles
The need for blood tests before every cycle
How the same drug is dosed in future
The ordinary side effects of treatment
Being straight with you
What this page cannot tell you
It cannot tell you whether your plan includes one of these drugs, or whether waiting for a result is safe in your situation. Both depend on the cancer, how fast it is growing and your overall health. Only the oncologist who wrote the plan can weigh that.
It cannot read a result for you
What your specific result means for your dose is a question for the oncologist who prescribes the drug. Reports use codes that are easy to misread, and the same gene can be reported in different ways by different laboratories. Never change or skip a dose because of something you read online.
Who this does not apply to
Most people on cancer treatment will never need this test. Many chemotherapy drugs, and most immunotherapy and targeted medicines, have no gene test before them. The evidence is also thinner for Indian patients, because most studies so far were done abroad and checked the gene versions common there.
This is a test about how you handle a medicine. It is separate from a test for inherited cancer risk and from a test on the tumour itself.Commonly believed
Four worries families have about asking, and what is true
"If I ask for a test, the doctor will think I do not trust them."
Oncologists are asked about tests every day. A question about your own safety is part of good care. If the test is not relevant to your drugs, you will simply be told so.
"If the test is not available, treatment has to wait."
Not usually. Doctors have long kept these drugs safe without the test by starting carefully, checking blood counts before each cycle and adjusting the dose. That decision is the oncologist's to make.
"A normal result means the drug will be gentle on me."
A normal result removes one specific cause of a severe reaction. Ordinary side effects still happen, and blood tests before each cycle are still needed.
"This test will also show whether my children could get cancer."
It will not. It reads only the genes that handle a drug. Inherited cancer risk needs a different test, arranged through genetic counselling.
Questions we are asked
Common questions about asking for a drug-gene test
Is it too late to ask if treatment has already started?
Not necessarily. The result still helps if the same drug continues or is used again later. If you have already had several cycles without severe side effects, a test is less likely to change the current plan. Your oncologist can tell you whether it is still worth doing.
How long does the result take?
It differs between laboratories. Samples taken in a district may first travel to a laboratory in a city. Ask when the sample is taken how long the report is expected to take, so your oncologist can decide whether to wait or start carefully.
Will insurance or Aarogyasri pay for the test?
Cover varies by policy and by scheme, and the test is often paid for by the family. Ask the billing desk before the sample is taken, not afterwards. A written estimate from the laboratory helps if you plan to claim it back from an insurer.
Can I get the test done privately without telling my doctor?
It is better not to. Your oncologist knows which gene matters for your drugs, and the result is only useful if it reaches the person setting the dose. A test ordered without that link can check the wrong gene or arrive too late to help.
What happens if my result shows a weak gene?
Your oncologist may lower the starting dose and raise it carefully, watch your blood counts more closely, or choose a different drug. The cancer is still treated. Do not change any dose on your own, even if the report seems to suggest it.
Should my brothers and sisters be tested too?
They may share the same gene version, because it is inherited. A result only matters for them if they are ever prescribed the same drug. There is no urgency, but it is worth telling them so they can mention it to a doctor one day.
Is this the same as the test on my tumour?
No. A tumour test looks for changes inside the cancer to help choose a treatment. A drug-gene test looks at genes you were born with to help set a safe dose. Families often think one was done when it was the other, so ask which test is meant.
Will I need to repeat the test for a later treatment?
No. The genes you were born with do not change, so one result holds for life. Keep a copy of the report and show it to any doctor who prescribes a new medicine, including doctors outside cancer care.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
Sources
- Clinical Pharmacogenetics Implementation Consortium (CPIC) — CPIC Guideline for Fluoropyrimidines and DPYD
- U.S. Food and Drug Administration — Table of Pharmacogenomic Biomarkers in Drug Labeling
- MedlinePlus — Pharmacogenetic Tests
- MedlinePlus Genetics — What is pharmacogenomics?
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Which cancer drugs have a gene test before themThe full list of drug and gene pairsWhy this testing is not routine yet in IndiaWhy nobody may offer it unless you askCost of drug-gene testingWhat to budget for before you askCarrying your pharmacogenomic result for future careHow to keep the result useful for life
Talk to us
Not sure whether your treatment plan needs a gene test?
Bring the list of drugs in your plan and we will help you find out whether any has a gene test before it. One helpline serves every CION centre.