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Together is a new resource for anyone affected by pediatric cancer - patients and their parents, family members, and friends.
Learn MoreJuvenile myelomonocytic leukemia (JMML) is a rare blood and bone marrow cancer that affects young children.
JMML occurs most often in children younger than age 4. About 10% of cases are in infants younger than 3 months.
Each year 1–2 children out of 1 million are diagnosed with JMML in the United States. That is 25–50 a year.
JMML occurs when bone marrow makes too many white blood cells called monocytes and myelocytes. The cells build up in the liver, spleen, bone marrow, and blood. When this happens, the blood does not work as it should. The body cannot fight infection as well.
JMML can be aggressive. Stem cell transplant is the only treatment that can cure JMML. But in 15% of cases, JMML will go away on its own without treatment. Doctors closely watch these cases.
Boys are twice as likely as girls to have JMML.
About 90% of children with JMML have changes in certain genes that cause the cancer. These changes are called mutations.
Learn more about leukemia and lymphoma causes, treatment, and side effects.
The most common mutated genes are:
| Gene | Percentage of cases | Features | Treatment |
|---|---|---|---|
| PTPN11 Germline (passed down) | 35-40% | - Mild disease - This gene change is linked to Noonan syndrome. |
Wait and watch or mild chemotherapy |
| PTPN11 Somatic (happens later) | - High chance of relapse
- Aggressive disease |
Stem cell transplant | |
| NF-1 (Germline) | 10% | - Children are usually age 5 or older at diagnosis. - Aggressive disease - They may have a higher platelet count and more bone marrow blasts than children with other subtypes of JMML. - Café-au-lait spots on skin (flat, brown patches) |
Stem cell transplant |
| CBL (Germline) | 15% | - May have 1 or more café-au-lait spots on skin - In some cases, the disease goes away without treatment. |
- Watch and wait in some cases - Stem cell transplant may be an option if the disease progresses. |
| KRAS (Germline) | - Mild disease | Wait and watch or mild chemotherapy | |
| KRAS (Somatic) | 10% | - Occurs mostly in infants - Often linked to monosomy 7 - Aggressive disease - Low risk of relapse after stem cell transplant |
Stem cell transplant |
| NRAS (Germline) |
15% | In some cases, the leukemia will go away without treatment. This usually occurs in infants or in cases with G12S mutation. | - Close monitoring in cases that are likely to go away on their own - Stem cell transplant may be an option. |
| NRAS (Somatic) | There is a high relapse rate after stem cell transplant. This usually occurs in older children with high levels of fetal hemoglobin. | Stem cell transplant |
Symptoms of JMML include:
Diagnosis of JMML can be challenging. JMML has symptoms like those of viral or bacterial infections and other childhood leukemias and blood disorders.
Chromosomal and genetic testing is important because the type of mutation can help decide treatment.
Tests to diagnose JMML include:
Treatment ranges from watchful observation to hematopoietic cell transplantation.
Doctors prescribe treatment based on how well patients are predicted to respond. This approach is called risk-adapted or risk-stratified.
The course of the disease and treatment response varies widely. Doctors may use age, level of fetal hemoglobin, and platelet count in part to help predict these things. Most children require transplant. In about 15% of cases, the disease will eventually resolve on its own without treatment.
Low risk includes patients with inherited mutation of PTPN11 (Noonan syndrome) or CBL (CBL syndrome). Sometimes these cases go into remission without treatment.
Doctors closely watch these patients. Patients may have chemotherapy if they develop symptoms such as an enlarged spleen and frequent infections.
Intermediate risk includes patients with a somatic NRAS mutation who are younger than 1.
Doctors closely watch these patients or treat them with chemotherapy. The drug azacytidine is approved for use in JMML.
Stem cell transplant may also be an option. It is the only treatment for high-risk JMML that offers hope of a cure. Patients must have a suitable donor to get this treatment.
High risk may include patients with somatic KRAS, NF1, or PTPN11 mutations. These cases are either predicted to resist treatment (refractory) or likely to come back (relapse).
Doctors may prescribe chemotherapy with the drugs fludarabine and cytarabine.
Stem cell transplant is a possible treatment. Sometimes this procedure is followed by an infusion of natural killer cells, a type of white blood cell. Chemotherapy may be an option. In limited cases, targeted therapy may be an option.
Stem cell transplant should occur as soon as possible after diagnosis. That is because successful transplant rates are highest in younger children. If JMML comes back, a second stem cell transplant and natural killer cell infusion may be successful.
Umbilical cord blood transplants are also a treatment option.
Other treatments may include:
Children with inherited syndromes may have different treatment than children with somatic mutations.
Stem cell transplant successfully treats more than 50% of cases.
JMML comes back in about 35–40% of children who go into remission with a transplant. Doctors may suggest a second transplant.
Stem cell transplants can have long-term side effects. These may include problems with growth, puberty, fertility, and organ function. Your care team can offer more details.
It is important to have regular follow-up appointments. Patients should also have good health habits. These include eating healthy foods, doing regular physical activities, and getting enough sleep.
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Reviewed: April 2023