Chronic myeloid leukemia (CML) is a type of cancer that affects blood-forming cells in the bone marrow. If a person does not respond to other forms of treatment or the illness progresses beyond the initial stages, a doctor may suggest a bone marrow transplant.
In a healthy person, the blood-forming cells in the bone marrow can grow and become red blood cells, white blood cells, or platelets.
In a person with CML, atypical immature blood cells called blasts grow and spread uncontrollably in the bone marrow and crowd out other types of blood cells.
Before a bone marrow transplant, a person will receive high doses of chemotherapy to kill leukemia cells and sometimes also a low dose of radiation therapy. These treatments will destroy normal bone marrow cells along with leukemia cells.
After these treatments, a person can receive a stem cell transplant. Stem cells are able to form blood and restore the bone marrow.
This article looks at what CML is, bone marrow transplants for CML, whether it is an effective treatment, and the risks of this treatment. Read on to also learn about alternative treatments for CML and the outlook for this type of cancer.
Leukemia refers to cancers of the blood cells. These cancers develop in blood-forming tissues, such as bone marrow, which produces cells that later develop into red and white blood cells and platelets.
- Red blood cells transport oxygen from the lungs to organs and tissues throughout the body.
- White blood cells help the body fight infections.
- Platelets help form clots to stop bleeding.
When a person has leukemia, their bone marrow produces large amounts of atypical cells, most often white blood cells. These atypical cells build up in the bone marrow and blood, and they crowd out other types of blood cells.
In CML, also known as chronic myelogenous leukemia, a genetic change happens in the myeloid stem cells, which make platelets, red blood cells, and most white blood cells. This genetic change leads to the atypical BCR-ABL gene, also known as the Philadelphia chromosome, which causes CML.
The CML cells grow, multiply, and build up in the bone marrow. Then they spread into the blood. Over time, the CML cells can reach and settle in other parts of the body, such as the spleen.
Although CML is a slow-moving cancer, it can develop into a fast-growing leukemia in later phases that is difficult to treat.
While bone marrow transplants used to be a mainstay in the treatment of CML, they are becoming less common since the development of the effective medication called tyrosine kinase inhibitors (TKIs). TKIs can put CML into remission for many years.
A doctor may suggest a bone marrow transplant, also known as a stem cell transplant, if:
- a person with CML does not respond well to targeted therapy with a TKI, which blocks the enzyme tyrosine kinase that causes the bone marrow to produce too many blasts
- the CML has progressed to the accelerated or blast crisis phase
An allogeneic stem cell transplant uses stem cells from a donor whose tissue type closely matches that of the person receiving the transplant.
The most effective donors are usually close family members, such as a sibling. However, a person can find a donor through a national registry, which is referred to as a matched unrelated donor (MUD) transplant.
Doctors collect the stem cells by harvesting the bone marrow of the donor, who in this case is not the person receiving the transplant. They then freeze the bone marrow until they are ready to transplant it to the patient.
After receiving high dose chemotherapy and sometimes radiation therapy, the patient receives the thawed donated bone marrow through infusion.
An allogeneic transplant
However, not every person with CML will be a good candidate for this type of treatment. It can have severe complications, especially in people who have other health problems or who are older.
In an allogeneic transplant, cells from a donor create immune cells, which may help kill CML cells that remain after chemotherapy and radiation therapy. This is called the graft-versus-cancer effect.
Risks include the following:
- Immune cells that attack cancer cells may also attack healthy cells in an individual. This is called graft-versus-host disease and can be life threatening. It can also be lifelong.
- The transplant may not be successful, and the donor cells could be destroyed or die before settling into the patient’s bone marrow.
- Previous infections may surface, which the immune system may be unable to suppress.
- The chemotherapy involved in the transplant also may have several side effects.
A person with CML may need to receive treatment at a specialized center with doctors who are experts in treating individuals with CML. Before treatment, doctors may perform two tests:
- Affected cells: Doctors may test to determine whether a person’s myeloid or lymphoid cells are the cause of their CML, which will influence the treatment method.
- BCR-ABL1 kinase domain mutation analysis: Doctors may check part of the BCR-ABL1 gene for mutations. Certain mutations could make the gene more or less susceptible to treatment with TKIs.
Alternative treatments to bone marrow transplantation may include:
- targeted therapy with TKIs, such as dasatinib, nilotinib, or imatinib mesylate
- high dose chemotherapy
- chemotherapy as palliative care to help improve a person’s quality of life
However, these treatments are not really alternatives, but rather treatments that doctors may utilize in order to allow time to arrange for the transplant.
The outlook for people with CML who receive a diagnosis in the earlier phases of the cancer is very good, with a life expectancy of only 3 years less than that of the general population.
Treatments such as TKIs and allogeneic transplantation, as well as other advances, have greatly improved the outlook associated with CML.
Successful allogeneic transplants are the only known cure for CML, and they potentially provide an outlook similar to that of a person with healthy blood cells.
However, without any treatment, CML can be fatal, with a survival rate of only 2–3 years. Early diagnosis and treatment are greatly beneficial to a person’s outlook.
CML is a type of cancer that affects blood-forming cells in the bone marrow. In a person with CML, atypical blood cells grow and spread in the bone marrow and crowd out other types of blood cells.
One type of treatment for CML is a bone marrow, or stem cell, transplant in which a donor’s bone marrow is harvested and then transplanted into the patient.
An allogeneic transplant can be an effective treatment and is the only known cure for CML. However, there are risks involved, such as the donated cells rejecting a person’s body.
That said, a successful allogeneic transplant can cure CML.