Key Points for This Section

Juvenile myelomonocytic leukemia is a childhood disease in which too many myelocytes and monocytes (immature white blood cells) are made in the bone marrow. Possible signs of juvenile myelomonocytic leukemia include fever, feeling very tired, and weight loss. Certain factors affect prognosis (chance of recovery) and treatment options.

Juvenile myelomonocytic leukemia is a childhood disease in which too many myelocytes and monocytes (immature white blood cells) are made in the bone marrow.

Juvenile myelomonocytic leukemia is a rare childhood cancer that occurs more often in children younger than 2 years. Children who have neurofibromatosis type 1 and males have an increased risk of developing juvenile myelomonocytic leukemia.

In JMML, the body tells too many blood stem cells to develop into two types of white blood cells called myelocytes and monocytes. Some of these blood stem cells never become mature white blood cells. These immature white blood cells are called blasts. Over time, the myelocytes, monocytes, and blasts crowd out the red blood cells and platelets in the bone marrow. When this happens, infection, anemia, or easy bleeding may occur.

Possible signs of juvenile myelomonocytic leukemia include fever, feeling very tired, and weight loss.

These and other symptoms may be caused by JMML. Other conditions may cause the same symptoms. A doctor should be consulted if any of the following problems occur:

• Fever for no known reason.
• Having infections, such as bronchitis or tonsillitis.
• Feeling very tired.
• Easy bruising or bleeding.
• Skin rash.
• Painless swelling of the lymph nodes in the neck, underarm, stomach, or groin.
• Pain or a feeling of fullness below the ribs.

Certain factors affect prognosis (chance of recovery) and treatment options.

The prognosis (chance of recovery) and treatment options for JMML depend on the following:

• The age of the child at diagnosis.
• The number of platelets in the blood.
• The amount of a certain type of hemoglobin in red blood cells.

Glossary Terms

A condition in which the number of red blood cells is below normal.

An immature blood cell.

A tissue with red blood cells, white blood cells, platelets, and other substances suspended in fluid called plasma. Blood takes oxygen and nutrients to the tissues, and carries away wastes.

The soft, sponge-like tissue in the center of most bones. It produces white blood cells, red blood cells, and platelets.

Inflammation (swelling and reddening) of the bronchi.

A term for diseases in which abnormal cells divide without control and can invade nearby tissues. Cancer cells can also spread to other parts of the body through the blood and lymph systems. There are several main types of cancer. Carcinoma is cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord.

The process of identifying a disease, such as cancer, from its signs and symptoms.

An increase in body temperature above normal (98.6 degrees F), usually caused by disease.

The area where the thigh meets the abdomen.

The substance inside red blood cells that binds to oxygen in the lungs and carries it to the tissues.

Invasion and multiplication of germs in the body. Infections can occur in any part of the body and can spread throughout the body. The germs may be bacteria, viruses, yeast, or fungi. They can cause a fever and other problems, depending on where the infection occurs. When the body’s natural defense system is strong, it can often fight the germs and prevent infection. Some cancer treatments can weaken the natural defense system.

A rare form of childhood leukemia in which cancer cells often spread into tissues such as the skin, lung, and intestines. Also called JMML.

A rounded mass of lymphatic tissue that is surrounded by a capsule of connective tissue. Lymph nodes filter lymph (lymphatic fluid), and they store lymphocytes (white blood cells). They are located along lymphatic vessels. Also called lymph gland.

A type of immune cell that is made in the bone marrow and travels through the blood to tissues in the body where it becomes a macrophage. Macrophages surround and kill microorganisms, ingest foreign material, remove dead cells, and boost immune responses. A monocyte is a type of white blood cell and a type of phagocyte.

A rare genetic condition that causes brown spots and tumors on the skin, freckling in skin areas not exposed to the sun, tumors on the nerves, and developmental changes in the nervous system, muscles, bone, and skin. Also called NF1.

A tiny piece of a cell found in the blood that breaks off from a large cell found in the bone marrow. Platelets help wounds heal and prevent bleeding by forming blood clots. Also called thrombocyte.

The likely outcome or course of a disease; the chance of recovery or recurrence.

A cell that carries oxygen to all parts of the body. Also called erythrocyte and RBC.

A cell from which other types of cells develop. For example, blood cells develop from blood-forming stem cells.

An organ that is part of the digestive system. The stomach helps digest food by mixing it with digestive juices and churning it into a thin liquid.

An indication that a person has a condition or disease. Some examples of symptoms are headache, fever, fatigue, nausea, vomiting, and pain.

A type of immune cell. Most white blood cells are made in the bone marrow and are found in the blood and lymph tissue. White blood cells help the body fight infections and other diseases. Granulocytes, monocytes, and lymphocytes are white blood cells. Also called leukocyte and WBC.