Once the chromosome number of the leukemia has been established, the leukemic cell is analyzed for structural rearrangements or translocations. The transfer of segment of one chromosome to anther chromosome results in a translocation. Translocations within the leukemia cell have long been known to infer response to therapy and prognosis. The most common translocation is t(12:21), occurring in 20% to 25% of childhood ALL cases. This translocation can only be detected using molecular analysis and confers a favorable prognosis. Another common translocation is t(1:19), with a frequency of 3% to 6% among childhood ALL cases. Less common translocation are t(4:11), and t(9:22), which both infer a pooere prognosis.