ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: The dual colour FISH assay that we designed and initially tested in all samples contained the BAC clones RP11-83J21 and RP11-323H21; the former targets the 3' end of ABL1 gene incorporating the whole of the coding region at 9q34.12 and was thus selected to detect the BCR/ABL1 fusion gene, while the latter targets a region 730 Kb downstream of the ABL1 gene and is present within the proximal breakpoint cluster region as identified in Ph negative BCR/ABL1 positive CML [13].