How Does Hematopoietic Stem Cell Transplant Work for Leukemia? (2026 Update)

Hematopoietic stem cell transplant is a treatment in which high-dose chemotherapy clears out diseased bone marrow so that healthy stem cells can be introduced to rebuild the blood system. It is considered as a way to lower relapse risk in cases such as high-risk acute leukemia, where chemotherapy alone carries a high chance of relapse.

Key Takeaways

• Hematopoietic stem cell transplant clears out the bone marrow and rebuilds it with healthy stem cells; the transplant itself is not surgery but is closer to an intravenous infusion.
• For high-risk acute leukemia—cases judged to carry a high relapse risk with chemotherapy alone—an allogeneic transplant (using a donor's cells) is the more common option.
• The donor's immune cells can be expected to attack any remaining cancer cells, but that same immune activity can also attack the patient's own body, causing graft-versus-host disease (GVHD).
• Engraftment, when the new cells take hold, usually takes about 2 to 4 weeks. Total stay abroad, including a 3-to-6-week hospital admission, generally runs 6 to 8 weeks, and for allogeneic transplants patients are often monitored for around 100 days.
• Korea's 5-year relative survival rate for leukemia is 55.7% (National Cancer Registry statistics, 2019–2023). This is a nationwide figure, not the result of any single institution, and outcomes vary considerably by subtype and risk group.

Why Is Stem Cell Transplant Effective for Leukemia?

• In acute leukemia, induction chemotherapy is first used to clear cancer cells from the bone marrow. If the patient falls into a high-risk group, moving on to an allogeneic hematopoietic stem cell transplant is often preferred over additional chemotherapy alone. This is because transplant aims for two effects at once, going beyond simply rebuilding the marrow.
• First, high-dose chemotherapy (conditioning) eliminates as many residual cancer cells in the marrow as possible. Second, in allogeneic transplant, the donor's immune cells add a further effect by attacking any cancer cells that remain. Combined, these two effects reduce relapse risk in cases where chemotherapy alone would carry a high chance of relapse.
• However, this same immune mechanism can attack the patient's skin, gut, and liver, leading to graft-versus-host disease, which is managed and balanced with immunosuppressive medication. This combination of benefit and burden is what sets allogeneic transplant apart from autologous transplant.

What Is the Actual Sequence of the Transplant Process?

• Step 1: In the first 1–2 weeks after arrival, staging tests are performed along with checks of heart, lung, liver, and kidney function and infection screening. For allogeneic transplant, donor tissue-matching (HLA) testing and health screening are carried out at the same time.
• Step 2: A central venous catheter is placed for chemotherapy and transfusions, and the patient undergoes about one week of conditioning chemotherapy to clear out the diseased marrow.
• Step 3: On the scheduled day, the hematopoietic stem cells are infused intravenously. This is not surgery but closer to a transfusion, and it is completed within a matter of tens of minutes.
• Step 4: The patient spends 2 to 4 weeks in a sterile isolation room while waiting for engraftment. Fever, mouth sores, and low blood counts are common during this period and are managed with transfusions and antibiotics.
• Step 5: Once engraftment is confirmed, the patient is discharged but does not return home immediately, instead staying within walking distance of the hospital for frequent outpatient follow-up. For allogeneic transplants, monitoring for GVHD and infection is often set at around 100 days.

If a Sibling Isn't a Match, Does That Rule Out Transplant?

• Not necessarily. Donors are searched for in this order: siblings, half-matched (haploidentical) donors such as parents or children, unrelated donors, and cord blood. Even without a fully matched sibling, options remain such as haploidentical transplant, unrelated donor search, and cord blood.
• Korea has accumulated substantial experience with haploidentical transplants, which helps reduce situations where treatment is stalled due to an inability to find a donor. Which pathway is actually feasible depends on the type of disease, the patient's age, and the urgency of treatment, so individual review is needed.

FAQ — How Severe Are the Side Effects After Transplant?

During the conditioning period, nausea, mouth sores, diarrhea, hair loss, and severe fatigue are common, and when blood counts drop, the risk of infection and bleeding rises. Graft-versus-host disease, a complication unique to allogeneic transplant, can present as skin rash, diarrhea, elevated liver enzymes, and dryness of the eyes and mouth—sometimes appearing suddenly early on, and sometimes developing into a chronic form months later. Recovery of strength and immune function can take anywhere from several months to over a year, and many patients need to be revaccinated afterward.

FAQ — How Much Does This Transplant Improve Survival?

How much a transplant helps varies greatly by subtype and risk group, so it cannot be summed up in a single number. For reference, Korea's overall 5-year relative survival rate for leukemia is 55.7% (National Cancer Registry statistics 2019–2023, National Cancer Information Center). This is a nationwide figure combining acute and chronic cases—it is not the outcome of any specific institution, nor is it a prediction of any individual's result. Since whether or not to transplant can greatly affect the course of disease in high-risk groups, whether transplant is needed for your specific risk group should be decided in consultation with your medical team.

Sources and Notes

• This article was written based on notes on blood cancer and hematopoietic stem cell transplant (National Cancer Information Center, NCCN patient guidelines, Medical Korea, National Cancer Registry statistics 2019–2023, SEER 2016–2022).
• This content is provided for general medical information purposes only. Diagnosis, treatment methods, and outcomes may vary depending on the individual's condition. Accurate diagnosis and treatment decisions should always be made in consultation with a medical professional.