Medical Oncologist
CION Cancer Clinics
Why a related stem cell donor must be screened first | CION Cancer Clinics
A brother, sister or parent can be a perfect tissue match and still carry the inherited gene fault that raised the patient's risk of leukaemia. Their cells could carry that risk into the patient's new marrow. This page explains why related donors are screened when an inherited cause is suspected, what can go wrong without it, and what screening can and cannot show. At CION Cancer Clinics, our oncologists plan screening and care for families with an inherited cancer syndrome, explained in plain words.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- Why can a matched relative not simply donate?
- What can go wrong if a carrier donates?
- What does the transplant team weigh before choosing a relative?
- The screening terms, in plain language
- What donor screening can and cannot show
- Four things families tell us, and what is actually true
- What this page cannot tell you
- Common questions about screening a related donor
The short answer
Why can a matched relative not simply donate?
Because a relative shares genes with the patient, and may share the same inherited fault that raised the risk of leukaemia. Cells from a carrier can bring that risk straight back into the patient's new marrow. Screening the donor first is how the transplant team avoids this.
Families share more than a tissue match
For most inherited blood cancer conditions, a parent passes the fault on. Each brother or sister then has a one in two chance of carrying it, whether or not they are a good tissue match. The two things are inherited separately. A perfect match tells you nothing about the fault.
Why this is now taken seriously
Doctors have reported patients who developed a new blood cancer in the donated cells, and donors whose stem cells could not be collected in the usual way. The reports are few, and studies so far are small. They have been consistent enough that expert guidance now recommends testing a related donor whenever an inherited cause is known or suspected.
Screening is about protecting the patient and the donor. It is not a judgement on the family.The risks screening avoids
What can go wrong if a carrier donates?
None of these is common. Each is serious enough to be worth a simple test to avoid.
A new blood cancer in the donated cells
The transplanted marrow carries the fault from the start. Over time, it can develop MDS or leukaemia of its own. Doctors call this donor-derived disease.
A new marrow that does not work well
Some inherited conditions weaken the stem cells themselves. The donor may give fewer cells than expected, and the new marrow may be slow to produce blood counts.
A hidden problem in the donor
Occasionally, screening finds that a donor who felt well already has low counts or an early blood disorder. That donor then needs care of their own, not a donation procedure.
A sibling who is mildly affected
In recessive conditions such as Fanconi anaemia, where a child inherits one faulty copy from each parent, a brother or sister can be affected but undiagnosed. This is more likely where parents are related by blood.
Cousin and uncle-niece marriages are still common in some communities, so this question is asked often in India.Not sure whether this applies to you?
Ask an oncologistHow the decision is made
What does the transplant team weigh before choosing a relative?
How strong the suspicion is
A known fault in the patient settles it. Clues such as a young age at diagnosis, a relative with leukaemia or lifelong low platelets raise the question even without a result.
Whether the family's fault is known
If the patient's fault has been found, each relative can be tested for that exact change. If it has not, screening relies on blood counts, a blood film and the family story, which is less certain.
How urgent the transplant is
Some patients cannot wait long. The team balances the time testing takes against the time the disease allows.
What other donors exist
If an unrelated or another family donor is available, the team can afford to be cautious with a relative whose status is uncertain.
Words you will hear
The screening terms, in plain language
- Donor-derived disease
- A blood disorder that starts in the donated cells after transplant, rather than a return of the patient's original leukaemia.
- Engraftment
- The point at which donated stem cells settle in the marrow and start making blood. Poor engraftment means this is slow or incomplete.
- Stem cell collection
- Gathering stem cells from the donor's blood after injections that push them out of the marrow, or directly from the hip bone.
- Dominant inheritance
- One faulty copy from one parent is enough to raise the risk. Most inherited leukaemia conditions work this way.
- Recessive inheritance
- A child must inherit a faulty copy from both parents to be affected. Parents usually carry one copy each and stay well.
- Carrier
- Someone who has the fault. For a dominant condition, a carrier is usually not used as a donor for a relative.
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Side by side
What donor screening can and cannot show
Screening can show
Screening cannot show
Whether the donor carries the family's known fault
A fault nobody has found yet in the patient
Whether the donor's blood counts are normal today
Whether the donor will ever develop a blood cancer
Whether donation is safe for the donor
Whether the transplant itself will succeed
Which other relatives should be offered testing
How any relative feels about being tested
Commonly believed
Four things families tell us, and what is actually true
"A brother is family, so his cells must be the safest choice."
A brother may be the closest tissue match, but he is also the person most likely to share an inherited fault. Safety depends on both questions, not just the match.
"She feels perfectly healthy, so she cannot be carrying anything."
Many carriers feel well and have normal counts for years. Only a gene test for the family's fault can say whether a relative carries it.
"Donor screening is only about infections."
Infection checks are done for every donor. Gene screening is a separate step, added only when an inherited cause is known or suspected.
"Registry donors are riskier because nobody knows their family."
An unrelated donor is very unlikely to carry your family's particular fault. That is one reason a well-matched registry donor can be the better choice in these families.
Being straight with you
What this page cannot tell you
It cannot tell you whether a particular relative is safe to use as a donor. That is decided by the transplant team, who see the patient's reports, the donor's results and the urgency together. A page like this can only explain the reasoning.
It cannot read a donor's gene result
What a specific variant means for donation is a question for the counsellor who ordered the test and the transplant team. A result the laboratory cannot yet classify is discussed case by case, not decided from a gene name.
Who this does not apply to
Most related donors need only the standard tissue typing, health and infection checks. If the patient's leukaemia shows no inherited clues, gene screening of relatives usually adds nothing. Research on the best way to screen donors is still developing, and practice varies between centres. The process for arranging these tests is described on our page about testing before a family donation.
If you have been told a relative cannot donate and do not understand why, it is fair to ask the team to explain it again.Questions we are asked
Common questions about screening a related donor
Is a sibling more likely to carry the fault than a stranger?
Yes. A brother or sister shares parents with the patient, so they may have inherited the same fault. An unrelated donor is very unlikely to carry it. That is why screening is aimed at relatives, not registry donors.
Can a parent donate if the fault came from them?
Usually not. A parent who carries the fault would pass the same risk into the patient's new marrow. Testing both parents often shows which side the fault came from, and the other parent may still be considered.
What if the patient's own fault has not been found?
Then screening cannot target one exact change. The team relies on the donor's blood counts, a blood film and the family story. When the suspicion is strong, they may prefer an unrelated donor instead.
What happens to a donor who is found to carry it?
They are usually not used as the donor. They are offered genetic counselling and, depending on the gene, regular blood counts of their own. Their children may also want to know whether to be tested later.
Is screening needed for a half-matched donor too?
Yes, if an inherited cause is suspected. Parents, children and half-matched siblings are all blood relatives, so the same question applies to each of them before they are chosen.
Does screening delay the transplant?
It can if it starts late. When the patient's own test is sent early and an unrelated donor search runs at the same time, screening a relative rarely holds things up.
Could a donor's result affect their insurance?
India has no dedicated law on genetic discrimination, so it is fair for a donor to ask this before testing. A counsellor can explain what the result would and would not reveal, and who would see it.
Where do we start?
Ask the haematologist whether an inherited cause has been considered for the patient. If it has, ask which relatives should be tested and in what order. The CION helpline can direct you to the right team.
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)
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Sources
- GeneReviews (NCBI) — RUNX1 Familial Platelet Disorder with Associated Myeloid Malignancies
- NHS — Stem cell and bone marrow transplants
- National Cancer Institute — Stem Cell Transplants in Cancer Treatment
- MedlinePlus Genetics — What are the different ways a genetic condition can be inherited?
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
Testing before a family stem cell donationThe practical steps, in the order they happenInherited predisposition to leukaemia and MDSWhich gene faults are behind thisBone marrow failure syndromes and cancer riskFanconi anaemia and why siblings are checkedLow platelets running in a familyA common clue that a donor may share the fault
Talk to us
Told a relative needs screening before they donate?
Tell us what the transplant team has said and which relatives have offered to donate. We will explain the reasoning and help you arrange counselling if it is needed. One helpline serves every CION centre.