This test is useful in cases of Acute Lymphoblastic Leukemia (ALL) with a suspected TEL/AML translocation. A chimeric product is formed as a result of translocation between the the helix-loop-helix domain of TEL on chromosome 12 fused to AML-1 (RUNX1) gene on chromosome 21, the DNA-binding subunit of the AML-1/CBF beta transcription factor complex. The fused protein formed gives rise to ALL. The test can help in detection of this particular defect using FISH technique.