Stem Cell Transplant for Chronic Myelomonocytic Leukemia (CMML)

A stem cell transplant (SCT), also known as a bone marrow transplant (BMT), is an intense treatment that offers the best chance to cure chronic myelomonocytic leukemia (CMML), if it can be done.

SCT can have serious, even life-threatening side effects, so many people with CMML might not be able to get this treatment.

What is stem cell transplant and how is it used to treat CMML?

For stem cell transplant (SCT), a person gets high-dose chemotherapy, often along with radiation to their entire body. This kills the cells in the bone marrow, including the leukemia cells. The person is then given new, healthy blood-forming stem cells, which settle in the bone marrow and start making new blood cells.

The main types of stem cell transplant (SCT) are:

• Allogeneic SCT (uses donor blood stem cells)
• Autologous SCT (uses a person’s own blood stem cells)

Allogeneic SCT is the type of stem cell transplant used for CMML.

A less intense type of allogeneic transplant, called a non-myeloablative transplant (mini-transplant) may also be an option for some people.

Allogeneic stem cell transplant as a treatment for CMML

If you have an allogeneic stem cell transplant to treat CMML, you will first get chemo and possibly radiation to destroy your bone marrow. You will then get blood-forming stem cells from another person (a 'donor').

This is the type of SCT used for CMML, if it can be done. The results are best when the donor’s cell type is closely matched to your own and the donor is closely related to you, such as a sibling.

If a closely related family member is not a full match, a matched, unrelated donor may be used as the source of the stem cells. Partially matched unrelated donors or half-matched family members may also be an option.

Side effects of allogeneic SCT

Allogeneic SCTs can have serious, even life-threatening, side effects. This includes prolonged low blood cell counts that can make a person very vulnerable to infections, bleeding, and other problems.

Because of these risks, an allogeneic SCT isn't likely to be a good option for people who are older and/or have other major health problems. While an allogeneic SCT offers the best chance to cure some people with CMML, many people with CMML aren't able to get this treatment.

Non-myeloablative transplant (mini-transplant) as a treatment for CMML

This less intense type of allogeneic transplant may be an option for some people with CMML, especially those who might not be able to tolerate high doses of chemo and/or radiation.

For this treatment, the doses of chemo and/or radiation are lower than those used for a standard allogeneic transplant. These doses aren't high enough to kill all the bone marrow cells, but they kill enough to allow the donor cells to take hold and grow in the bone marrow. These donor cells can then help wipe out any remaining leukemia cells.

The lower doses of chemo and/or radiation cause fewer side effects, which makes this type of transplant easier for older people to tolerate. But it can still have some serious side effects.

Autologous stem cell transplant

In an autologous stem cell transplant, a person 'donates' some of their own blood stem cells (from either their blood or bone marrow). These are then frozen until they are needed. After the bone marrow is destroyed with chemo and/or radiation, the person gets their own stem cells back.

Autologous transplants aren't routinely used to treat CMML because the person's own blood stem cells are likely to contain leukemia cells, which they would get back after the transplant.