and have headaches, dizziness, or a fast heartbeat. The number of RBCs is measured by a blood test measuring the hemoglobin level. A low level of RBCs is called anemia. Platelets are the blood-clotting cells that are needed to stop bleeding and to form a clot. If the level of platelets in the blood is low, there is an increased chance of bleeding and bruising. A rash that looks like small red-purple freckles also may be seen. These freckles are called petechiae . A low level of platelets is called thrombocytopenia .
n WHAT ARE THE TYPES OF LEUKEMIA? There are several different types of leukemia, with two main classifications based on how quickly cells grow: acute leukemia and chronic leukemia. Acute leukemia develops from young, immature cells called blasts . The blast cells divide frequently, causing the leukemia cells to grow and accumulate very quickly. The main types of acute leukemia are: • Acute lymphoblastic leukemia (ALL)—a cancer that occurs in the lymphocytes, affecting either the T or B lymphocytes. This is the most common type of childhood leukemia. • Acute myeloid leukemia (AML)—a cancer that occurs in the myeloid cells, usually affecting the WBCs; however, in some cases, it may involve the RBCs or platelets. • A less common kind of cancer— biphenotypic leukemia —has features of both ALL and AML. Chronic leukemia develops more slowly and occurs in more mature, abnormal cells. This type of leukemia is seen more often in adults than in children. The two main types of chronic leukemia are chronic myelogenous leukemia (CML) and chronic lymphoblastic leukemia (CLL). Treatment for chronic leukemia is very different than treatment for acute leukemia, and it is not discussed in this booklet. n HOW COMMON IS ACUTE LYMPHOBLASTIC LEUKEMIA (ALL)? ALL is the most common cancer seen in children. It often is seen in young children and young adults, with most children diagnosed between 2 and 5 years of age. About 2,400 people develop ALL each year. Caucasian children are more likely to have ALL than African American children, and the likelihood is highest in Hispanic children. ALL is more common in boys than in girls. About 85% of children who develop ALL will survive. Leukemia involving B-cell lymphocytes is the most common. Among children with ALL, 85% will have B-cell leukemia.
There are three types of B-cell ALL: • Early pre-B (very immature B cells) • Pre-B (immature B cells) • B-cell (mature B cells, also called Burkitt’s lymphoma).
Early pre-B and pre-B ALL are treated in the same way. Burkitt’s lymphoma is only seen in 1%–2% of children with ALL; this type of ALL requires different, more intensive treatment that is given over a shorter period of time. Leukemia involving the T-cell lymphocyte is seen in about 15% of childhood leukemia. At the time the diagnosis is made, children with T-cell ALL have a higher WBC count and a mass in the chest. Most commonly, T-cell ALL affects older children and boys.
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