Juvenile chronic myelomonocytic leukaemia – Diagnostics – Overview of Information and Clinical Research

Juvenile chronic myelomonocytic leukaemia (JMML) is a rare blood cancer affecting very young children, typically under the age of four. Diagnosing this condition involves a careful combination of blood tests, bone marrow examinations, and specialized genetic testing to distinguish it from other childhood illnesses and blood disorders.

Introduction: Who Should Seek Diagnostics

Parents and caregivers should consider seeking medical evaluation if their young child displays concerning symptoms that persist or worsen over weeks to months. Because JMML (juvenile myelomonocytic leukaemia) is a rare and slowly developing blood cancer, symptoms often appear gradually rather than suddenly. This can make early recognition challenging, as many signs overlap with common childhood illnesses.^[1]

Children who should undergo diagnostic testing are those experiencing a combination of symptoms such as persistent tiredness and lethargy, frequent infections that take longer than usual to clear, unexplained fevers, easy bruising or nosebleeds, pale skin, or a noticeable increase in belly size due to an enlarged liver or spleen. Some children may develop skin rashes, cough and wheezing, or show signs of irritability that make them harder to settle. If a child has jumped a nappy or trouser size quickly without a clear reason, this could indicate organ enlargement and warrants medical attention.^[3]^[10]

It is particularly important to seek prompt evaluation for children with certain genetic conditions. Those diagnosed with neurofibromatosis type 1, a genetic disorder affecting nerve tissue growth, or Noonan syndrome, a condition involving developmental abnormalities, face a higher risk of developing JMML. Between 10 and 15 out of every 100 cases of JMML occur in children with neurofibromatosis type 1, making regular monitoring advisable for these patients.^[3]^[1]

While JMML is extremely rare, affecting only about one to two children per million each year, early diagnosis can make a significant difference in treatment planning and outcomes. The disease most commonly appears in children younger than two years old, with boys affected slightly more often than girls. Parents should not delay seeking medical advice if their child shows a pattern of symptoms that does not improve or continues to develop over time.^[6]^[3]

⚠️ Important

JMML develops slowly over weeks to months, so children may have very few symptoms at first. This gradual onset means parents might not immediately recognize something is wrong. If your child seems persistently unwell without a clear cause, or if symptoms slowly worsen despite treatment for common illnesses, consult your doctor for a thorough evaluation.

Classic Diagnostic Methods

Diagnosing JMML requires a series of specialized tests, as the condition shares features with other childhood blood disorders and infections. Doctors must carefully evaluate the child’s symptoms, medical history, and test results to reach an accurate diagnosis. Most diagnostic tests are not painful, though young children may need to remain still during some procedures, which can be challenging.^[3]

Blood Tests

The diagnostic journey typically begins with blood tests, which are the most fundamental tool for detecting JMML. A complete blood count measures the numbers and types of cells circulating in the blood. In children with JMML, doctors look for specific patterns that set this disease apart from other conditions. One key finding is an elevated number of monocytes, a type of white blood cell that helps fight infection. The blood must show a monocyte count of at least 1 × 10⁹ per liter, with monocytes making up at least 10 percent of all white blood cells.^[6]^[7]

Blood tests also reveal other important information. Doctors examine the proportion of immature blood cells called blasts and promonocytes in both the blood and bone marrow. For a JMML diagnosis, these immature cells must make up less than 20 percent of the total cell count. This distinguishes JMML from acute forms of leukaemia, where blast counts are much higher. Additionally, blood tests measure red blood cell counts, which are often low in children with JMML, causing anaemia. This explains why affected children may look pale, feel tired, and have a racing heart even during light activity.^[4]^[7]

Another critical aspect of blood testing involves measuring platelet counts. Platelets help blood clot, and children with JMML often have too few of them. Low platelet counts explain the easy bruising, nosebleeds, and prolonged bleeding from minor cuts that many children experience. Blood chemistry tests, including liver and kidney function assessments, help doctors understand how the disease is affecting other organs in the body.^[1]^[4]

A particularly important blood test looks for increased levels of hemoglobin F, also called fetal hemoglobin. This is a type of hemoglobin normally present before birth but usually replaced by adult hemoglobin after birth. Elevated hemoglobin F levels are commonly seen in children with JMML and help support the diagnosis.^[2]

Bone Marrow Tests

While blood tests provide vital clues, examining the bone marrow directly offers the most detailed picture of what is happening inside the body. The bone marrow is the soft, spongy tissue inside bones where blood cells are made. In JMML, abnormal cells crowd the bone marrow, preventing it from producing enough healthy red blood cells, white blood cells, and platelets.^[3]

A bone marrow examination typically involves two procedures performed at the same time. The first is a bone marrow aspiration, where doctors use a needle to withdraw a small sample of liquid bone marrow. The second is a bone marrow biopsy, which removes a tiny piece of bone containing marrow. These samples are then examined under a microscope to look at the types and proportions of cells present. Doctors count the number of blasts and promonocytes, check the appearance of cells, and assess how crowded the marrow is with abnormal cells.^[1]

Genetic and Molecular Testing

Modern diagnosis of JMML relies heavily on genetic testing, as the disease is fundamentally caused by changes in genes that control cell growth. Many children with JMML have mutations in genes that are part of the RAS pathway, a series of molecular signals that regulate how cells multiply and develop. Testing for these genetic changes has become a standard part of the diagnostic criteria.^[2]^[6]

The most commonly mutated genes in JMML include PTPN11, NRAS, KRAS, NF1, and CBL. Finding a mutation in any one of these genes is sufficient to confirm the diagnosis when combined with the appropriate clinical and laboratory findings. In some cases, children carry these genetic changes in all their body cells, not just blood cells. This is called a germline mutation and is often associated with conditions like Noonan syndrome. Germline mutations sometimes lead to a temporary form of the disease that may resolve on its own without intensive treatment.^[2]^[7]

Genetic testing also helps doctors understand how aggressive the disease might be. Children with certain mutation patterns, particularly those involving the RAS pathway combined with additional genetic changes, may have a more challenging course and higher risk of the disease progressing. Understanding which genes are altered helps guide treatment decisions and provides information about prognosis.^[2]

Tests to Rule Out Other Conditions

A crucial part of diagnosing JMML involves ensuring that the child does not have a different condition that looks similar. Doctors must specifically exclude chronic myeloid leukaemia (CML), another blood cancer that can occur in children. This is done by testing for the BCR-ABL fusion gene, a genetic abnormality that causes CML. Children with JMML do not have this fusion gene, so its absence helps confirm the diagnosis.^[7]^[2]

Similarly, testing must show the absence of rearrangements in the KMT2A gene, which is associated with certain types of acute leukaemia. Blood and bone marrow samples undergo detailed analysis to ensure these genetic markers are not present. This careful exclusion process is essential because different blood cancers require very different treatments.^[7]

Doctors must also distinguish JMML from non-cancerous conditions that cause similar symptoms. These include immunodeficiency disorders where the immune system does not work properly, viral infections such as cytomegalovirus or Epstein-Barr virus, intrauterine infections acquired before birth, and hemophagocytic lymphohistiocytosis, a severe immune system disorder. Each of these conditions can cause fever, enlarged organs, and abnormal blood counts, making careful testing essential to reach the correct diagnosis.^[2]

Additional Diagnostic Criteria

For children whose genetic testing does not reveal mutations in the commonly affected genes, or when genetic testing is not available, doctors use additional laboratory criteria to support the diagnosis. One important test measures how bone marrow cells respond to a protein called granulocyte-macrophage colony-stimulating factor (GM-CSF). In JMML, bone marrow cells are abnormally sensitive to this protein, causing them to grow more readily than normal cells when exposed to it in laboratory tests.^[7]^[2]

Clinical evidence of organ infiltration, most commonly enlargement of the spleen (splenomegaly), is another required criterion. Nearly all children with JMML have an enlarged spleen at diagnosis, often accompanied by an enlarged liver. This enlargement occurs because abnormal blood cells accumulate in these organs. Doctors can detect this through physical examination, where they feel the abdomen, or through imaging tests like ultrasound.^[6]^[7]

Diagnostics for Clinical Trial Qualification

When children with JMML are considered for enrollment in clinical trials, they typically undergo the same standard diagnostic procedures used for initial diagnosis. Clinical trials are research studies testing new treatments or approaches to managing the disease. Because these studies must carefully track how well treatments work and monitor for side effects, they require precise and thorough documentation of each child’s disease characteristics before treatment begins.^[2]

For trial enrollment, doctors verify that all diagnostic criteria for JMML have been met according to the most current international standards. This includes confirming the presence of a monocyte count of at least 1 × 10⁹ per liter, demonstrating that blasts and promonocytes make up less than 20 percent of blood and bone marrow cells, documenting the absence of the BCR-ABL fusion gene and KMT2A rearrangements, and identifying mutations in RAS pathway genes when present.^[7]

Additional tests may be required depending on the specific trial. Some studies focus on children with particular genetic mutations, so comprehensive genetic testing becomes essential. Others may require assessment of how well a child’s organs are functioning before starting experimental treatments, including heart function tests, kidney function tests, and lung function tests. Imaging studies such as chest X-rays or abdominal ultrasounds may be performed to document the extent of organ enlargement or disease spread.^[2]

Clinical trials often require a baseline assessment of the child’s overall health status and any symptoms they are experiencing. This helps researchers measure whether new treatments improve quality of life. Doctors may use standardized questionnaires or scoring systems to document symptoms like fatigue, fever, pain, and ability to participate in normal activities. Blood tests measuring inflammation markers, nutritional status, and immune function may also be part of the baseline evaluation.^[2]

Some trials test treatments aimed at specific molecular targets identified through genetic testing. For these studies, detailed molecular profiling of the cancer cells may be required. This involves analyzing not just the five main genes commonly mutated in JMML, but also looking for additional genetic changes that might influence how the disease behaves or responds to treatment. Advanced testing techniques can identify patterns of DNA changes called epigenetic alterations, which affect how genes are turned on or off without changing the DNA sequence itself.^[2]

⚠️ Important

Participating in a clinical trial may give your child access to promising new treatments not yet widely available. However, trials have specific eligibility requirements and may involve additional testing. Your child’s medical team can help you understand whether a clinical trial is an appropriate option and explain what extra tests or procedures might be needed.

Before enrolling in any clinical trial, families receive detailed information about what tests will be performed, why they are necessary, and what they involve. Parents or guardians must provide informed consent, confirming they understand the study’s purpose, procedures, potential benefits, and risks. Throughout the trial, regular monitoring tests track the child’s response to treatment and watch for any complications. The frequency and types of these monitoring tests vary depending on the specific trial protocol and the treatment being studied.^[2]

Prognosis and Survival Rate

Prognosis

The outlook for children with JMML varies depending on several factors, but overall the disease remains challenging to treat. The course of JMML can be unpredictable, with some children experiencing a more aggressive form of the disease that progresses quickly, while others have a slower course. Certain characteristics identified at diagnosis help doctors estimate how the disease might behave.^[2]

Children with mutations in specific genes tend to have different outcomes. Those with germline mutations in genes like PTPN11, KRAS, or NRAS, which are present from birth and often associated with Noonan syndrome, may develop a transient form of the disease that sometimes resolves without intensive treatment. This represents a more favorable prognosis. In contrast, children with somatic mutations (changes that occur only in blood cells, not throughout the body) in RAS pathway genes often face a more aggressive disease course.^[2]

JMML carries an inherent risk of transformation to acute myeloid leukemia, a more aggressive blood cancer. Without treatment, this transformation can occur relatively quickly. The disease can also spread beyond the blood and bone marrow to affect other parts of the body. When abnormal cells spread to the brain, children may develop headaches, seizures, balance problems, or vision difficulties. Spread to lymph nodes in the chest can cause breathing problems and chest pain.^[1]

Clinical features at diagnosis also influence prognosis. Children presenting with very high white blood cell counts, severe anemia, low platelet counts, or extensive organ infiltration may face greater challenges. Age at diagnosis plays a role as well, with the median age of presentation being approximately 1.8 years. The disease occurs more commonly in boys than girls, with a male-to-female ratio of about 2.5 to 1.^[6]

Survival rate

JMML has historically been associated with poor outcomes, though advances in treatment have improved survival rates in recent years. Allogeneic hematopoietic stem cell transplant (HSCT), where a child receives healthy stem cells from a donor, remains the only known cure for JMML. With this treatment approach, approximately 50 percent of patients achieve long-term survival.^[2]

However, even after successful transplant, the disease can return. Relapses are common, and when they occur, a second stem cell transplant can salvage about one-third of these patients. The overall survival depends heavily on whether a child is eligible for transplant and how well they tolerate the procedure. Success rates are generally better when transplant is performed early in the disease course, before extensive complications develop.^[2]

For children treated with chemotherapy alone, outcomes are generally less favorable. Standard chemotherapy can sometimes stabilize the disease temporarily but rarely leads to long-term remission without transplant. Some children with less aggressive forms of JMML, particularly those with certain germline mutations, may achieve long-term remission with chemotherapy alone, but this represents a minority of cases.^[2]

A study examining outcomes from bone marrow transplantation between 1982 and 1992 reported that among 12 children who underwent the procedure, long-term remission was achieved in three patients, with two others in remission at shorter follow-up periods. This illustrates both the potential for cure with transplant and the significant challenges that remain in treating this disease.^[8]

It is important for families to understand that statistics represent averages across many patients and may not predict the outcome for any individual child. Each child’s situation is unique, influenced by their specific genetic mutations, overall health, response to treatment, and availability of a suitable stem cell donor. The medical team caring for your child can provide more personalized information based on their particular circumstances.^[2]

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