NORD gratefully acknowledges Prof. Franco Locatelli, Full Professor of Pediatrics, University of Pavia, Director, Department of Pediatric Hematology and Oncology, IRCCS Ospedale Pediatrico Bambino Gesù, Rome, Italy, for assistance in the preparation of this report.
Juvenile myelomonocytic leukemia (JMML) is a rare pediatric form of blood cancer. JMML predominately affects young children, most often developing in children under the age of 4. The male/female ratio of affected children is 2-3:1.The disorder is characterized by the uncontrolled growth of an immature form of a specific type of white blood cell known as monocyte precursors. These abnormal cells accumulate in the bone marrow crowding out other healthy cells. The bone marrow produces specialized cells (hematopoietic stem cells) that grow and eventually develop into red blood cells, white blood cells and platelets. These cells are released into the bloodstream to travel throughout the body and perform specific functions. Red blood cells deliver oxygen to the body; white blood cells help the body to fight infection; and platelets allow the body to form clots to stop bleeding. When abnormal cells accumulate in the bone marrow, they can affect the production and function of these healthy blood cells. Abnormal cells can accumulate in other tissues and organs of the body such as the lungs, skin, liver, and intestines. JMML is an aggressive and difficult to treat disease. Currently, the main therapeutic option is allogeneic hematopoietic stem cell transplantation. The exact, underlying cause of JMML is unknown.
Over the years, several different classification systems have been used to define JMML. Currently, the World Health Organization (WHO) classifies JMML as an overlap myelodysplastic syndrome/myeloproliferative disorder because JMML shares characteristics with both of these groups of disorders. Myelodysplastic syndromes are defined as a group of disorders that are characterized by disordered development of blood cells in the bone marrow. Myeloproliferative disorders are defined as a group of disorders characterized by the overproduction (proliferation) of the three main blood cell lines, red or white blood cells or platelets. The first case of JMML was described in the medical literature in 1924.
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