Chromosome translocations

Sometimes genetic material is exchanged between chromosomes in leukemia cells. This is called a translocation. Translocations are very common in childhood ALL, and some of these are known to affect prognosis. Examples are:

• Movement of the TEL (ETV6) gene on chromosome 12 to the AML1 (CBFA2) gene on chromosome 21. This is called the TEL-AML1 fusion and is found most often in children between the ages of 2 and 9. Children with this translocation usually have very good outcomes.

• The Philadelphia chromosome, called t(9;22), is found in approximately 3 to 4 percent of children with ALL. It is associated with a poor prognosis, especially in older children with high white blood counts and a slow response to treatment.

• Translocations involving the MLL gene are found in 6 percent of children with ALL. The most common MLL translocation is t(4;11). This occurs most often in infants with CNS disease and high white blood counts at diagnosis. The t(11;19) translocation is associated with a poor outcome in infants but a favorable outcome in older children with T-cell leukemia and this translocation.

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