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UGT1A1 beyond irinotecan: the other cancer drugs it affects | CION Cancer Clinics
UGT1A1 is the gene most people meet before irinotecan chemotherapy. It also matters for a small group of other cancer medicines. Some, like sacituzumab govitecan, carry the same active substance and can build up. Others, like nilotinib and pazopanib, block the gene's work and raise bilirubin, which can look like liver damage when it is not. This page explains both, and why a common Indian variant matters. At CION Cancer Clinics, our team helps carriers and their families plan checks, next steps and support after a genetic result.
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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
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On this page
- Does UGT1A1 matter for drugs other than irinotecan?
- Which cancer drugs does UGT1A1 affect besides irinotecan?
- What happens if bilirubin goes up during treatment?
- The UGT1A1 words you may see, in plain language
- Two ways UGT1A1 can matter
- What this page cannot tell you
- Four things people assume about UGT1A1
- Common questions about UGT1A1 and cancer drugs
The short answer
Does UGT1A1 matter for drugs other than irinotecan?
Yes, for a small group of cancer medicines. UGT1A1 matters in two quite different ways. Some drugs are cleared by the UGT1A1 enzyme, so a slow-working gene lets them build up. Other drugs block the enzyme, so bilirubin rises in the blood and the eyes can turn yellow, even when the liver is healthy.
What the gene actually does
UGT1A1 makes a liver enzyme that attaches a chemical tag to certain substances so the body can wash them out in bile. Its most important everyday job is clearing bilirubin, the yellow pigment made when old red blood cells break down. It also clears the active form of irinotecan and a handful of other medicines.
Why this matters in India
A common version of the gene, called UGT1A1 *28, makes the enzyme work more slowly. It is common in Indian populations. People with two copies often have Gilbert syndrome, a harmless condition in which bilirubin runs a little high, especially when fasting or unwell. Many never know they have it until a cancer drug or a routine blood test shows it.
Gilbert syndrome is not a liver disease. It becomes relevant only when certain medicines are involved.The drugs involved
Which cancer drugs does UGT1A1 affect besides irinotecan?
The American drug regulator lists UGT1A1 on the labels of several cancer medicines. These are the ones most likely to come up.
Sacituzumab govitecan
An antibody-drug conjugate used in some advanced breast cancers. It delivers the same active substance as irinotecan straight to cancer cells. People with two copies of UGT1A1 *28 face a higher risk of a low white cell count and other side effects, so they are watched more closely.
Belinostat
A drug used in some T-cell lymphomas. It is cleared by UGT1A1, and its label advises a lower starting dose for people with two copies of UGT1A1 *28.
Nilotinib
A daily tablet for chronic myeloid leukaemia. It blocks UGT1A1, so bilirubin often rises, and more so in people with two copies of the slow version.
What it usually means
- Yellow eyes without liver damage
- Liver enzymes often normal
- A dose change is sometimes needed
Pazopanib
A tablet for kidney cancer and some soft tissue sarcomas. It can raise bilirubin in people with Gilbert syndrome. Its label asks doctors to tell that harmless rise apart from genuine liver injury.
Not sure whether this applies to you?
Ask an oncologistWhen bilirubin rises
What happens if bilirubin goes up during treatment?
A routine blood test shows the rise
Liver blood tests are checked regularly on these drugs. A raised bilirubin, or yellow eyes you notice yourself, starts the process.
The team checks which kind of bilirubin
A rise in the unprocessed, indirect form with normal liver enzymes points towards UGT1A1. A rise alongside abnormal liver enzymes points towards liver injury.
Your history and genes are considered
A past diagnosis of Gilbert syndrome, earlier mild jaundice when ill, or a UGT1A1 result all help the team read the rise correctly.
A decision is made about the drug
A harmless rise may simply be watched while treatment continues. A rise that suggests liver injury may mean a pause, a lower dose or a different drug.
On your report
The UGT1A1 words you may see, in plain language
- UGT1A1
- A gene that makes a liver enzyme which tags bilirubin and some drugs so the body can remove them.
- Bilirubin
- A yellow pigment from worn-out red blood cells. High levels turn the eyes and skin yellow.
- Gilbert syndrome
- A harmless inherited condition in which bilirubin runs slightly high. It usually needs no treatment.
- UGT1A1 *28
- The common slow version of the gene, found widely in India. One copy has a mild effect. Two copies have a larger one.
- UGT1A1 *6
- Another slow version, more common in East Asian populations and less common in India.
- SN-38
- The active substance released by both irinotecan and sacituzumab govitecan. UGT1A1 is what clears it.
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Side by side
Two ways UGT1A1 can matter
The drug is cleared by UGT1A1
The drug blocks UGT1A1
Irinotecan, sacituzumab govitecan, belinostat
Nilotinib, pazopanib, and atazanavir outside cancer care
The worry is drug build-up and low counts
The worry is a bilirubin rise that looks alarming
A slow result may change the starting dose
A slow result changes how a rise is read
Ask: should my starting dose change?
Ask: is this my liver or my genes?
Being straight with you
What this page cannot tell you
It cannot tell you whether your own raised bilirubin is harmless. That needs your full liver tests, your history and your oncologist's judgement. What your specific UGT1A1 result means is a question for the doctor or genetic counsellor who ordered the test.
The evidence is thinner beyond irinotecan
For irinotecan, the link with UGT1A1 has been studied for many years. For the other drugs, the evidence is smaller, and labels differ between countries in how strongly they advise testing. Studies in Indian patients on these newer drugs are few.
Who this does not apply to
Most cancer medicines are not affected by UGT1A1, and most people do not need this test. It matters only if you are starting one of the drugs above, or if unexplained yellow eyes appear on one of them. It is an inherited test and says nothing about cancer risk.
It is not a tumour test
UGT1A1 is read from your own inherited DNA. Tests on the tumour, which guide targeted drugs, answer a different question altogether.
Commonly believed
Four things people assume about UGT1A1
"UGT1A1 only matters for irinotecan."
Irinotecan is the best known example, but it is not the only one. Sacituzumab govitecan carries the same active substance, and several other cancer drugs either depend on the enzyme or block it.
"Yellow eyes on nilotinib always mean the liver is being damaged."
Often they do not. Nilotinib blocks the enzyme that clears bilirubin, so the pigment rises even in a healthy liver. Your team checks the liver enzymes to tell the two apart. Report yellow eyes promptly and never stop the tablet yourself.
"Gilbert syndrome is a liver disease that needs treatment."
It is a harmless inherited variation. The liver works normally. It needs no treatment, but it is worth telling every doctor who prescribes you one of these drugs.
"I should have a UGT1A1 test before any chemotherapy."
Only a small number of drugs are affected. For most chemotherapy the result changes nothing, and your oncologist will suggest the test only when it is relevant.
Questions we are asked
Common questions about UGT1A1 and cancer drugs
I was told I have Gilbert syndrome. Should my oncologist know?
Yes. Tell your oncologist before treatment starts, and mention it again if a new drug is added. It helps the team read your liver tests correctly and decide whether any starting dose needs a second look. Keep any old report that mentions it.
Is a UGT1A1 test needed before sacituzumab govitecan?
It is not always required. Some teams test first and some monitor closely instead, especially early in treatment. If you already know your UGT1A1 result from earlier irinotecan treatment, share it, because the same active substance is involved.
My bilirubin went up on nilotinib. Should I stop the tablets?
No. Do not stop on your own. Tell your team, who will check the rest of your liver tests. A bilirubin rise on nilotinib is common and often harmless, but only your doctor can decide whether the dose needs changing.
Why does my bilirubin rise when I am not eating well?
With a slow UGT1A1 gene, bilirubin climbs further during fasting, dehydration, illness and stress. During cancer treatment, poor appetite and vomiting are common, so the rise can look bigger than usual. Tell your team if you have been fasting before a blood test.
Can UGT1A1 testing be done in Hyderabad?
Yes. It is the same test commonly used before irinotecan, and several laboratories in the city offer it from a blood sample. Ask your oncologist whether it is useful for the drug you are starting before arranging it.
Is UGT1A1 *28 passed on in families?
Yes. Each child inherits one copy of the gene from each parent, so brothers, sisters and children may share your result. It carries no cancer risk, so relatives need no action unless they are prescribed one of these drugs.
Does the result need repeating for each new drug?
No. Your genes do not change, so one result lasts for life. What changes is which drug it is relevant to. Keep the report and show it whenever a new cancer medicine is started.
I had severe diarrhoea on irinotecan before. Does that matter now?
Yes, tell your team. If you are being offered sacituzumab govitecan, the same active substance is involved, and past severe reactions help the team plan the dose and how closely to watch you in the early weeks.
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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)
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Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- MedlinePlus Genetics — UGT1A1 gene
- MedlinePlus Genetics — Gilbert syndrome
- NCBI Medical Genetics Summaries — Irinotecan Therapy and UGT1A1 Genotype
- US Food and Drug Administration — Table of Pharmacogenomic Biomarkers in Drug Labeling
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-gene pairs in cancer careWhat a poor metaboliser result meansIf your report says two slow copiesIntermediate metaboliser results and dose adjustmentWhat one slow copy usually changesCarrying your pharmacogenomic result for future careMaking one test count for every future prescription
Talk to us
Worried about a bilirubin rise on treatment?
Bring your latest liver tests and any UGT1A1 report, and an oncologist will explain what the rise is likely to mean. One helpline serves every CION centre.