A progressive, malignant disease characterized by large numbers of immature white blood cells that resemble lymphoblasts.These cells can be found in the blood, the bone marrow, the lymph nodes, the spleen, and other organs.

Acute lymphocytic leukemia (A.L.L.) is responsible for 80% of the acute leukemias of childhood, with the peak incidenceoccurring between ages 3 and 7. A.L.L. also occurs in adults, where it comprises 20% of all adult leukemias. In acute leukemia,the malignant cell loses its ability to mature and specialize (differentiate) its function. These cells multiply rapidly and replacethe normal cells. Bone marrow failure occurs as malignant cells replace normal bone marrow elements. The person becomessusceptible to bleeding and infection because the normal blood cells are reduced in number.Most cases seem to have no apparent cause. However, radiation, some toxins such as benzene, and some chemotherapy agentsare thought to contribute to the induction of leukemia. Abnormalities in chromosomes may also play a role in the developmentof acute leukemia. Risk factors for acute leukemia include Down syndrome, a sibling with leukemia, and exposure to radiation,chemicals, and drugs. The incidence is 6 out of 100,000 people.

Because the cause of most cases is unknown, prevention of most cases is unknown. Minimizing exposure to toxins, radiation,chemicals, and so on may reduce risk.